Merge branch 'send' into 'main'

send emails See merge request etke.cc/postmoogle!30
2022-09-07 06:47:41 +00:00
parent a92b4c64ae 8823867ba5
commit 47767e2ab2
17 changed files with 828 additions and 95 deletions
--- a/README.md
+++ b/README.md
@@ -18,14 +18,25 @@ It can't be used with arbitrary email providers, but setup your own provider "wi
 - [x] Receive attachments
 - [x] Map email threads to matrix threads

+#### deep dive
+
+> features in that section considered as "nice to have", but not a priority
+
+- [ ] DKIM verification
+- [ ] SPF verification
+- [ ] DMARC verification
+- [ ] Blocklists 
+
 ### Send

- [ ] SMTP client
+- [x] SMTP client
+- [x] Send a message to matrix room with special format to send a new email
 - [ ] Reply to matrix thread sends reply into email thread
- [ ] Send a message to matrix room with special format to send a new email

 ## Configuration

+### 1. Bot (mandatory)
+
 env vars

 * **POSTMOOGLE_HOMESERVER** - homeserver url, eg: `https://matrix.example.com`
@@ -50,6 +61,148 @@ You can find default values in [config/defaults.go](config/defaults.go)

 </details>

+### 2. DNS (optional)
+
+The following configuration is needed only if you want to send outgoing emails via Postmoogle (it's not necessary if you only want to receive emails).
+
+**First**, add a new DMARC DNS record of the `TXT` type for subdomain `_dmarc` with a proper policy. The simplest policy you can use is: `v=DMARC1; p=quarantine;`.
+
+<details>
+<summary>Example</summary>
+
+```bash
+$ dig txt _dmarc.example.com
+
+; <<>> DiG 9.18.6 <<>> txt _dmarc.example.com
+;; global options: +cmd
+;; Got answer:
+;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57306
+;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
+
+;; OPT PSEUDOSECTION:
+; EDNS: version: 0, flags:; udp: 1232
+;; QUESTION SECTION:
+;_dmarc.example.com.			IN	TXT
+
+;; ANSWER SECTION:
+_dmarc.example.com.		1799	IN	TXT	"v=DMARC1; p=quarantine;"
+
+;; Query time: 46 msec
+;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
+;; WHEN: Sun Sep 04 21:31:30 EEST 2022
+;; MSG SIZE  rcvd: 79
+```
+
+</details>
+
+**Second**, add a new SPF DNS record of the `TXT` type for your domain that will be used with Postmoogle, with format: `v=spf1 ip4:SERVER_IP -all` (replace `SERVER_IP` with your server's IP address)
+
+<details>
+<summary>Example</summary>
+
+```bash
+$ dig txt example.com
+
+; <<>> DiG 9.18.6 <<>> txt example.com
+;; global options: +cmd
+;; Got answer:
+;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24796
+;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
+
+;; OPT PSEUDOSECTION:
+; EDNS: version: 0, flags:; udp: 1232
+;; QUESTION SECTION:
+;example.com.			IN	TXT
+
+;; ANSWER SECTION:
+example.com.		1799	IN	TXT	"v=spf1 ip4:111.111.111.111 -all"
+
+;; Query time: 36 msec
+;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
+;; WHEN: Sun Sep 04 21:35:04 EEST 2022
+;; MSG SIZE  rcvd: 255
+```
+
+</details>
+
+**Third**, add a new MX DNS record of the `MX` type for your domain that will be used with postmoogle. It should point to the same (sub-)domain.
+Looks odd, but some mail servers will refuse to interact with your mail server (and Postmoogle is already a mail server) without MX records.
+
+<details>
+<summary>Example</summary>
+
+```bash
+dig MX example.com
+
+; <<>> DiG 9.18.6 <<>> MX example.com
+;; global options: +cmd
+;; Got answer:
+;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12688
+;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
+
+;; OPT PSEUDOSECTION:
+; EDNS: version: 0, flags:; udp: 1232
+;; QUESTION SECTION:
+;example.com.			IN	MX
+
+;; ANSWER SECTION:
+example.com.		1799	IN	MX	10 example.com.
+
+;; Query time: 40 msec
+;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
+;; WHEN: Tue Sep 06 16:44:47 EEST 2022
+;; MSG SIZE  rcvd: 59
+```
+
+</details>
+
+**Fourth** (and the last one), add new DKIM DNS record of `TXT` type for subdomain `postmoogle._domainkey` that will be used with postmoogle.
+
+You can get that signature using the `!pm dkim` command:
+
+<details>
+<summary>!pm dkim</summary>
+
+DKIM signature is: `v=DKIM1; k=ed25519; p=OcVzOwAONDfgbJX/5vwzlXOs9gUDO0YKlXHaDnBJtXw=`.
+You need to add it to your DNS records (if not already):
+Add new DNS record with type = `TXT`, key (subdomain/from): `postmoogle._domainkey` and value (to):
+
+```
+v=DKIM1; k=ed25519; p=OcVzOwAONDfgbJX/5vwzlXOs9gUDO0YKlXHaDnBJtXw=
+```
+
+Without that record other email servers may reject your emails as spam, kupo.
+
+</details>
+
+<details>
+<summary>Example</summary>
+
+```bash
+$ dig TXT postmoogle._domainkey.example.com
+
+; <<>> DiG 9.18.6 <<>> TXT postmoogle._domainkey.example.com
+;; global options: +cmd
+;; Got answer:
+;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59014
+;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
+
+;; OPT PSEUDOSECTION:
+; EDNS: version: 0, flags:; udp: 1232
+;; QUESTION SECTION:
+;postmoogle._domainkey.example.com.	IN	TXT
+
+;; ANSWER SECTION:
+postmoogle._domainkey.example.com. 600	IN TXT  "v=DKIM1; k=ed25519; p=OcVzOwAONDfgbJX/5vwzlXOs9gUDO0YKlXHaDnBJtXw="
+
+;; Query time: 90 msec
+;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
+;; WHEN: Mon Sep 05 16:16:21 EEST 2022
+;; MSG SIZE  rcvd: 525
+```
+
+</details>
+
 ## Usage

 ### How to start
@@ -81,8 +234,9 @@ If you want to change them - check available options in the help message (`!pm h

 ---

-* **!pm mailboxes** - Show the list of all mailboxes
+* **!pm dkim** - Get DKIM signature
 * **!pm users** - Get or set allowed users patterns
+* **!pm mailboxes** - Show the list of all mailboxes
 * **!pm delete** &lt;mailbox&gt; - Delete specific mailbox

 </details>
--- a/bot/access.go
+++ b/bot/access.go
@@ -17,17 +17,24 @@ func parseMXIDpatterns(patterns []string, defaultPattern string) ([]*regexp.Rege
 	return utils.WildcardMXIDsToRegexes(patterns)
 }

-func (b *Bot) allowAnyone(actorID id.UserID, targetRoomID id.RoomID) bool {
-	return true
-}
-
-func (b *Bot) allowOwner(actorID id.UserID, targetRoomID id.RoomID) bool {
+func (b *Bot) allowUsers(actorID id.UserID) bool {
 	if len(b.allowedUsers) != 0 {
 		if !utils.Match(actorID.String(), b.allowedUsers) {
 			return false
 		}
 	}

+	return true
+}
+
+func (b *Bot) allowAnyone(actorID id.UserID, targetRoomID id.RoomID) bool {
+	return true
+}
+
+func (b *Bot) allowOwner(actorID id.UserID, targetRoomID id.RoomID) bool {
+	if !b.allowUsers(actorID) {
+		return false
+	}
 	cfg, err := b.getRoomSettings(targetRoomID)
 	if err != nil {
 		b.Error(context.Background(), targetRoomID, "failed to retrieve settings: %v", err)
@@ -45,3 +52,17 @@ func (b *Bot) allowOwner(actorID id.UserID, targetRoomID id.RoomID) bool {
 func (b *Bot) allowAdmin(actorID id.UserID, targetRoomID id.RoomID) bool {
 	return utils.Match(actorID.String(), b.allowedAdmins)
 }
+
+func (b *Bot) allowSend(actorID id.UserID, targetRoomID id.RoomID) bool {
+	if !b.allowUsers(actorID) {
+		return false
+	}
+
+	cfg, err := b.getRoomSettings(targetRoomID)
+	if err != nil {
+		b.Error(context.Background(), targetRoomID, "failed to retrieve settings: %v", err)
+		return false
+	}
+
+	return !cfg.NoSend()
+}
--- a/bot/bot.go
+++ b/bot/bot.go
@@ -13,6 +13,8 @@ import (
 	"maunium.net/go/mautrix/event"
 	"maunium.net/go/mautrix/format"
 	"maunium.net/go/mautrix/id"
+
+	"gitlab.com/etke.cc/postmoogle/utils"
 )

 // Bot represents matrix bot
@@ -25,6 +27,7 @@ type Bot struct {
 	rooms                   sync.Map
 	botcfg                  cache.Cache[botSettings]
 	cfg                     cache.Cache[roomSettings]
+	mta                     utils.MTA
 	log                     *logger.Logger
 	lp                      *linkpearl.Linkpearl
 	mu                      map[id.RoomID]*sync.Mutex
@@ -77,7 +80,7 @@ func (b *Bot) Error(ctx context.Context, roomID id.RoomID, message string, args

 	sentry.GetHubFromContext(ctx).CaptureException(err)
 	if roomID != "" {
-		b.SendError(ctx, roomID, message)
+		b.SendError(ctx, roomID, err.Error())
 	}
 }

--- a/bot/command.go
+++ b/bot/command.go
@@ -14,6 +14,8 @@ import (
 const (
 	commandHelp      = "help"
 	commandStop      = "stop"
+	commandSend      = "send"
+	commandDKIM      = "dkim"
 	commandUsers     = botOptionUsers
 	commandDelete    = "delete"
 	commandMailboxes = "mailboxes"
@@ -51,6 +53,11 @@ func (b *Bot) initCommands() commandList {
 			description: "Disable bridge for the room and clear all configuration",
 			allowed:     b.allowOwner,
 		},
+		{
+			key:         commandSend,
+			description: "Send email",
+			allowed:     b.allowSend,
+		},
 		{allowed: b.allowOwner}, // delimiter
 		// options commands
 		{
@@ -66,6 +73,15 @@ func (b *Bot) initCommands() commandList {
 			allowed:     b.allowOwner,
 		},
 		{allowed: b.allowOwner}, // delimiter
+		{
+			key: roomOptionNoSend,
+			description: fmt.Sprintf(
+				"Get or set `%s` of the room (`true` - enable email sending; `false` - disable email sending)",
+				roomOptionNoSend,
+			),
+			sanitizer: utils.SanitizeBoolString,
+			allowed:   b.allowOwner,
+		},
 		{
 			key: roomOptionNoSender,
 			description: fmt.Sprintf(
@@ -117,6 +133,11 @@ func (b *Bot) initCommands() commandList {
 			description: "Get or set allowed users",
 			allowed:     b.allowAdmin,
 		},
+		{
+			key:         commandDKIM,
+			description: "Get DKIM signature",
+			allowed:     b.allowAdmin,
+		},
 		{
 			key:         commandMailboxes,
 			description: "Show the list of all mailboxes",
@@ -146,6 +167,10 @@ func (b *Bot) handleCommand(ctx context.Context, evt *event.Event, commandSlice
 		b.sendHelp(ctx)
 	case commandStop:
 		b.runStop(ctx)
+	case commandSend:
+		b.runSend(ctx, commandSlice)
+	case commandDKIM:
+		b.runDKIM(ctx)
 	case commandUsers:
 		b.runUsers(ctx, commandSlice)
 	case commandDelete:
@@ -237,3 +262,49 @@ func (b *Bot) sendHelp(ctx context.Context) {

 	b.SendNotice(ctx, evt.RoomID, msg.String())
 }
+
+func (b *Bot) runSend(ctx context.Context, commandSlice []string) {
+	evt := eventFromContext(ctx)
+	if !b.allowSend(evt.Sender, evt.RoomID) {
+		return
+	}
+	to, subject, body, err := utils.ParseSend(commandSlice)
+	if err == utils.ErrInvalidArgs {
+		b.SendNotice(ctx, evt.RoomID, fmt.Sprintf(
+			"Usage:\n"+
+				"```\n"+
+				"%s send someone@example.com\n"+
+				"Subject goes here on a line of its own\n"+
+				"Email content goes here\n"+
+				"on as many lines\n"+
+				"as you want.\n"+
+				"```",
+			b.prefix))
+		return
+	}
+
+	cfg, err := b.getRoomSettings(evt.RoomID)
+	if err != nil {
+		b.Error(ctx, evt.RoomID, "failed to retrieve room settings: %v", err)
+		return
+	}
+
+	mailbox := cfg.Mailbox()
+	if mailbox == "" {
+		b.SendNotice(ctx, evt.RoomID, "mailbox is not configured, kupo")
+		return
+	}
+
+	from := mailbox + "@" + b.domain
+	ID := evt.ID.String()[1:] + "@" + b.domain
+	data := utils.
+		NewEmail(ID, "", subject, from, to, body, "", nil).
+		Compose(b.getBotSettings().DKIMPrivateKey())
+	err = b.mta.Send(from, to, data)
+	if err != nil {
+		b.Error(ctx, evt.RoomID, "cannot send email: %v", err)
+		return
+	}
+
+	b.SendNotice(ctx, evt.RoomID, "Email has been sent")
+}
--- a/bot/command_admin.go
+++ b/bot/command_admin.go
@@ -6,6 +6,7 @@ import (
 	"sort"
 	"strings"

+	"gitlab.com/etke.cc/go/secgen"
 	"maunium.net/go/mautrix/id"

 	"gitlab.com/etke.cc/postmoogle/utils"
@@ -130,3 +131,32 @@ func (b *Bot) runUsers(ctx context.Context, commandSlice []string) {
 	b.allowedUsers = allowedUsers
 	b.SendNotice(ctx, evt.RoomID, "allowed users updated")
 }
+
+func (b *Bot) runDKIM(ctx context.Context) {
+	evt := eventFromContext(ctx)
+	cfg := b.getBotSettings()
+	signature := cfg.DKIMSignature()
+	if signature == "" {
+		var private string
+		var derr error
+		signature, private, derr = secgen.DKIM()
+		if derr != nil {
+			b.Error(ctx, evt.RoomID, "cannot generate DKIM signature: %v", derr)
+			return
+		}
+		cfg.Set(botOptionDKIMSignature, signature)
+		cfg.Set(botOptionDKIMPrivateKey, private)
+		err := b.setBotSettings(cfg)
+		if err != nil {
+			b.Error(ctx, evt.RoomID, "cannot save bot options: %v", err)
+			return
+		}
+	}
+
+	b.SendNotice(ctx, evt.RoomID, fmt.Sprintf(
+		"DKIM signature is: `%s`.\n"+
+			"You need to add it to your DNS records (if not already):\n"+
+			"Add new DNS record with type = `TXT`, key (subdomain/from): `postmoogle._domainkey` and value (to):\n ```\n%s\n```\n"+
+			"Without that record other email servers may reject your emails as spam, kupo.",
+		signature, signature))
+}
--- a/bot/email.go
+++ b/bot/email.go
@@ -3,53 +3,32 @@ package bot
 import (
 	"context"
 	"errors"
+	"fmt"
 	"strings"

 	"maunium.net/go/mautrix/event"
-	"maunium.net/go/mautrix/format"
 	"maunium.net/go/mautrix/id"

 	"gitlab.com/etke.cc/postmoogle/utils"
 )

-// account data key
-const acMessagePrefix = "cc.etke.postmoogle.message"
+// account data keys
+const (
+	acMessagePrefix   = "cc.etke.postmoogle.message"
+	acLastEventPrefix = "cc.etke.postmoogle.last"
+)

 // event keys
 const (
 	eventMessageIDkey = "cc.etke.postmoogle.messageID"
 	eventInReplyToKey = "cc.etke.postmoogle.inReplyTo"
+	eventSubjectKey   = "cc.etke.postmoogle.subject"
+	eventFromKey      = "cc.etke.postmoogle.from"
 )

-func email2content(email *utils.Email, cfg roomSettings, threadID id.EventID) *event.Content {
-	var text strings.Builder
-	if !cfg.NoSender() {
-		text.WriteString("From: ")
-		text.WriteString(email.From)
-		text.WriteString("\n\n")
-	}
-	if !cfg.NoSubject() {
-		text.WriteString("# ")
-		text.WriteString(email.Subject)
-		text.WriteString("\n\n")
-	}
-	if email.HTML != "" && !cfg.NoHTML() {
-		text.WriteString(format.HTMLToMarkdown(email.HTML))
-	} else {
-		text.WriteString(email.Text)
-	}
-
-	parsed := format.RenderMarkdown(text.String(), true, true)
-	parsed.RelatesTo = utils.RelatesTo(cfg.NoThreads(), threadID)
-
-	content := event.Content{
-		Raw: map[string]interface{}{
-			eventMessageIDkey: email.MessageID,
-			eventInReplyToKey: email.InReplyTo,
-		},
-		Parsed: parsed,
-	}
-	return &content
+// SetMTA sets mail transfer agent instance to the bot
+func (b *Bot) SetMTA(mta utils.MTA) {
+	b.mta = mta
 }

 // GetMapping returns mapping of mailbox = room
@@ -67,7 +46,7 @@ func (b *Bot) GetMapping(mailbox string) (id.RoomID, bool) {
 }

 // Send email to matrix room
-func (b *Bot) Send(ctx context.Context, email *utils.Email) error {
+func (b *Bot) Send2Matrix(ctx context.Context, email *utils.Email) error {
 	roomID, ok := b.GetMapping(utils.Mailbox(email.To))
 	if !ok {
 		return errors.New("room not found")
@@ -87,8 +66,7 @@ func (b *Bot) Send(ctx context.Context, email *utils.Email) error {
 			b.setThreadID(roomID, email.MessageID, threadID)
 		}
 	}
-
-	content := email2content(email, cfg, threadID)
+	content := email.Content(threadID, cfg.ContentOptions())
 	eventID, serr := b.lp.Send(roomID, content)
 	if serr != nil {
 		return utils.UnwrapError(serr)
@@ -98,6 +76,7 @@ func (b *Bot) Send(ctx context.Context, email *utils.Email) error {
 		b.setThreadID(roomID, email.MessageID, eventID)
 		threadID = eventID
 	}
+	b.setLastEventID(roomID, threadID, eventID)

 	if !cfg.NoFiles() {
 		b.sendFiles(ctx, roomID, email.Files, cfg.NoThreads(), threadID)
@@ -105,6 +84,84 @@ func (b *Bot) Send(ctx context.Context, email *utils.Email) error {
 	return nil
 }

+func (b *Bot) getParentEmail(evt *event.Event) (string, string, string) {
+	content := evt.Content.AsMessage()
+	parentID := utils.EventParent(evt.ID, content)
+	if parentID == evt.ID {
+		return "", "", ""
+	}
+	parentID = b.getLastEventID(evt.RoomID, parentID)
+	parentEvt, err := b.lp.GetClient().GetEvent(evt.RoomID, parentID)
+	if err != nil {
+		b.log.Error("cannot get parent event: %v", err)
+		return "", "", ""
+	}
+	if parentEvt.Content.Parsed == nil {
+		perr := parentEvt.Content.ParseRaw(event.EventMessage)
+		if perr != nil {
+			b.log.Error("cannot parse event content: %v", perr)
+			return "", "", ""
+		}
+	}
+
+	to := utils.EventField[string](&parentEvt.Content, eventFromKey)
+	inReplyTo := utils.EventField[string](&parentEvt.Content, eventMessageIDkey)
+	if inReplyTo == "" {
+		inReplyTo = parentID.String()
+	}
+
+	subject := utils.EventField[string](&parentEvt.Content, eventSubjectKey)
+	if subject != "" {
+		subject = "Re: " + subject
+	} else {
+		subject = strings.SplitN(content.Body, "\n", 1)[0]
+	}
+
+	return to, inReplyTo, subject
+}
+
+// Send2Email sends message to email
+// TODO rewrite to thread replies only
+func (b *Bot) Send2Email(ctx context.Context, to, subject, body string) error {
+	var inReplyTo string
+	evt := eventFromContext(ctx)
+	cfg, err := b.getRoomSettings(evt.RoomID)
+	if err != nil {
+		return err
+	}
+	mailbox := cfg.Mailbox()
+	if mailbox == "" {
+		return fmt.Errorf("mailbox not configured, kupo")
+	}
+	from := mailbox + "@" + b.domain
+	pTo, pInReplyTo, pSubject := b.getParentEmail(evt)
+	inReplyTo = pInReplyTo
+	if pTo != "" && to == "" {
+		to = pTo
+	}
+	if pSubject != "" && subject == "" {
+		subject = pSubject
+	}
+
+	content := evt.Content.AsMessage()
+	if subject == "" {
+		subject = strings.SplitN(content.Body, "\n", 1)[0]
+	}
+	if body == "" {
+		if content.FormattedBody != "" {
+			body = content.FormattedBody
+		} else {
+			body = content.Body
+		}
+	}
+
+	ID := evt.ID.String()[1:] + "@" + b.domain
+	data := utils.
+		NewEmail(ID, inReplyTo, subject, from, to, body, "", nil).
+		Compose(b.getBotSettings().DKIMPrivateKey())
+	return b.mta.Send(from, to, data)
+}
+
 func (b *Bot) sendFiles(ctx context.Context, roomID id.RoomID, files []*utils.File, noThreads bool, parentID id.EventID) {
 	for _, file := range files {
 		req := file.Convert()
@@ -117,7 +174,7 @@ func (b *Bot) sendFiles(ctx context.Context, roomID id.RoomID, files []*utils.Fi
 			MsgType:   event.MsgFile,
 			Body:      req.FileName,
 			URL:       resp.ContentURI.CUString(),
-			RelatesTo: utils.RelatesTo(noThreads, parentID),
+			RelatesTo: utils.RelatesTo(!noThreads, parentID),
 		})
 		if err != nil {
 			b.Error(ctx, roomID, "cannot send uploaded file %s: %v", req.FileName, err)
@@ -152,3 +209,31 @@ func (b *Bot) setThreadID(roomID id.RoomID, messageID string, eventID id.EventID
 		}
 	}
 }
+
+func (b *Bot) getLastEventID(roomID id.RoomID, threadID id.EventID) id.EventID {
+	key := acLastEventPrefix + "." + threadID.String()
+	data := map[string]id.EventID{}
+	err := b.lp.GetClient().GetRoomAccountData(roomID, key, &data)
+	if err != nil {
+		if !strings.Contains(err.Error(), "M_NOT_FOUND") {
+			b.log.Error("cannot retrieve account data %s: %v", key, err)
+			return threadID
+		}
+	}
+
+	return data["eventID"]
+}
+
+func (b *Bot) setLastEventID(roomID id.RoomID, threadID id.EventID, eventID id.EventID) {
+	key := acLastEventPrefix + "." + threadID.String()
+	data := map[string]id.EventID{
+		"eventID": eventID,
+	}
+
+	err := b.lp.GetClient().SetRoomAccountData(roomID, key, data)
+	if err != nil {
+		if !strings.Contains(err.Error(), "M_NOT_FOUND") {
+			b.log.Error("cannot save account data %s: %v", key, err)
+		}
+	}
+}
--- a/bot/settings_bot.go
+++ b/bot/settings_bot.go
@@ -11,7 +11,9 @@ const acBotSettingsKey = "cc.etke.postmoogle.config"

 // bot options keys
 const (
-	botOptionUsers = "users"
+	botOptionUsers          = "users"
+	botOptionDKIMSignature  = "dkim.pub"
+	botOptionDKIMPrivateKey = "dkim.pem"
 )

 type botSettings map[string]string
@@ -40,6 +42,16 @@ func (s botSettings) Users() []string {
 	return []string{value}
 }

+// DKIMSignature (DNS TXT record)
+func (s botSettings) DKIMSignature() string {
+	return s.Get(botOptionDKIMSignature)
+}
+
+// DKIMPrivateKey keep it secret
+func (s botSettings) DKIMPrivateKey() string {
+	return s.Get(botOptionDKIMPrivateKey)
+}
+
 func (b *Bot) initBotUsers() ([]string, error) {
 	config := b.getBotSettings()
 	cfgUsers := config.Users()
--- a/bot/settings_room.go
+++ b/bot/settings_room.go
@@ -15,6 +15,7 @@ const acRoomSettingsKey = "cc.etke.postmoogle.settings"
 const (
 	roomOptionOwner     = "owner"
 	roomOptionMailbox   = "mailbox"
+	roomOptionNoSend    = "nosend"
 	roomOptionNoSender  = "nosender"
 	roomOptionNoSubject = "nosubject"
 	roomOptionNoHTML    = "nohtml"
@@ -42,6 +43,10 @@ func (s roomSettings) Owner() string {
 	return s.Get(roomOptionOwner)
 }

+func (s roomSettings) NoSend() bool {
+	return utils.Bool(s.Get(roomOptionNoSend))
+}
+
 func (s roomSettings) NoSender() bool {
 	return utils.Bool(s.Get(roomOptionNoSender))
 }
@@ -62,6 +67,21 @@ func (s roomSettings) NoFiles() bool {
 	return utils.Bool(s.Get(roomOptionNoFiles))
 }

+// ContentOptions converts room display settings to content options
+func (s roomSettings) ContentOptions() *utils.ContentOptions {
+	return &utils.ContentOptions{
+		HTML:    !s.NoHTML(),
+		Sender:  !s.NoSender(),
+		Subject: !s.NoSubject(),
+		Threads: !s.NoThreads(),
+
+		FromKey:      eventFromKey,
+		SubjectKey:   eventSubjectKey,
+		MessageIDKey: eventMessageIDkey,
+		InReplyToKey: eventInReplyToKey,
+	}
+}
+
 func (b *Bot) getRoomSettings(roomID id.RoomID) (roomSettings, error) {
 	cfg := b.cfg.Get(roomID.String())
 	if cfg != nil {
@@ -77,7 +97,9 @@ func (b *Bot) getRoomSettings(roomID id.RoomID) (roomSettings, error) {
 			// In such cases, just return a default (empty) settings object.
 			err = nil
 		}
-	} else {
+	}
+
+	if err == nil {
 		b.cfg.Set(roomID.String(), config)
 	}

--- a/go.mod
+++ b/go.mod
@@ -4,6 +4,7 @@ go 1.18

 require (
 	git.sr.ht/~xn/cache/v2 v2.0.0
+	github.com/emersion/go-msgauth v0.6.6
 	github.com/emersion/go-smtp v0.15.0
 	github.com/getsentry/sentry-go v0.13.0
 	github.com/jhillyerd/enmime v0.10.0
@@ -11,6 +12,7 @@ require (
 	github.com/mattn/go-sqlite3 v1.14.14
 	gitlab.com/etke.cc/go/env v1.0.0
 	gitlab.com/etke.cc/go/logger v1.1.0
+	gitlab.com/etke.cc/go/secgen v1.1.0
 	gitlab.com/etke.cc/linkpearl v0.0.0-20220831124140-598117f26c77
 	golang.org/x/net v0.0.0-20220826154423-83b083e8dc8b
 	maunium.net/go/mautrix v0.12.0
@@ -27,6 +29,7 @@ require (
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.16 // indirect
 	github.com/mattn/go-runewidth v0.0.12 // indirect
+	github.com/mikesmitty/edkey v0.0.0-20170222072505-3356ea4e686a // indirect
 	github.com/olekukonko/tablewriter v0.0.5 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/rivo/uniseg v0.2.0 // indirect
--- a/go.sum
+++ b/go.sum
@@ -6,10 +6,18 @@ github.com/cention-sany/utf7 v0.0.0-20170124080048-26cad61bd60a/go.mod h1:2GxOXO
 github.com/coreos/go-systemd/v22 v22.3.3-0.20220203105225-a9a7ef127534/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/emersion/go-message v0.11.2/go.mod h1:C4jnca5HOTo4bGN9YdqNQM9sITuT3Y0K6bSUw9RklvY=
+github.com/emersion/go-message v0.15.0/go.mod h1:wQUEfE+38+7EW8p8aZ96ptg6bAb1iwdgej19uXASlE4=
+github.com/emersion/go-milter v0.3.3/go.mod h1:ablHK0pbLB83kMFBznp/Rj8aV+Kc3jw8cxzzmCNLIOY=
+github.com/emersion/go-msgauth v0.6.6 h1:buv5lL8v/3v4RpHnQFS2IPhE3nxSRX+AxnrEJbDbHhA=
+github.com/emersion/go-msgauth v0.6.6/go.mod h1:A+/zaz9bzukLM6tRWRgJ3BdrBi+TFKTvQ3fGMFOI9SM=
 github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21 h1:OJyUGMJTzHTd1XQp98QTaHernxMYzRaOasRir9hUlFQ=
 github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21/go.mod h1:iL2twTeMvZnrg54ZoPDNfJaJaqy0xIQFuBdrLsmspwQ=
 github.com/emersion/go-smtp v0.15.0 h1:3+hMGMGrqP/lqd7qoxZc1hTU8LY8gHV9RFGWlqSDmP8=
 github.com/emersion/go-smtp v0.15.0/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
+github.com/emersion/go-textwrapper v0.0.0-20160606182133-d0e65e56babe/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
+github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
 github.com/getsentry/sentry-go v0.13.0 h1:20dgTiUSfxRB/EhMPtxcL9ZEbM1ZdR+W/7f7NWD+xWo=
 github.com/getsentry/sentry-go v0.13.0/go.mod h1:EOsfu5ZdvKPfeHYV6pTVQnsjfp30+XA7//UooKNumH0=
 github.com/go-errors/errors v1.0.1 h1:LUHzmkK3GUKUrL/1gfBUxAHzcev3apQlezX/+O7ma6w=
@@ -30,6 +38,7 @@ github.com/jhillyerd/enmime v0.10.0 h1:DZEzhptPRBesvN3gf7K1BOh4rfpqdsdrEoxW1Edr/
 github.com/jhillyerd/enmime v0.10.0/go.mod h1:Qpe8EEemJMFAF8+NZoWdpXvK2Yb9dRF0k/z6mkcDHsA=
 github.com/lib/pq v1.10.6 h1:jbk+ZieJ0D7EVGJYpL9QTz7/YW6UHbmdnZWYyK5cdBs=
 github.com/lib/pq v1.10.6/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
+github.com/martinlindhe/base36 v1.0.0/go.mod h1:+AtEs8xrBpCeYgSLoY/aJ6Wf37jtBuR0s35750M27+8=
 github.com/mattn/go-colorable v0.1.12/go.mod h1:u5H1YNBxpqRaxsYJYSkiCWKzEfiAb1Gb520KVy5xxl4=
 github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
 github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
@@ -41,6 +50,8 @@ github.com/mattn/go-runewidth v0.0.12 h1:Y41i/hVW3Pgwr8gV+J23B9YEY0zxjptBuCWEaxm
 github.com/mattn/go-runewidth v0.0.12/go.mod h1:RAqKPSqVFrSLVXbA8x7dzmKdmGzieGRCM46jaSJTDAk=
 github.com/mattn/go-sqlite3 v1.14.14 h1:qZgc/Rwetq+MtyE18WhzjokPD93dNqLGNT3QJuLvBGw=
 github.com/mattn/go-sqlite3 v1.14.14/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A/KQRfk6bU=
+github.com/mikesmitty/edkey v0.0.0-20170222072505-3356ea4e686a h1:eU8j/ClY2Ty3qdHnn0TyW3ivFoPC/0F1gQZz8yTxbbE=
+github.com/mikesmitty/edkey v0.0.0-20170222072505-3356ea4e686a/go.mod h1:v8eSC2SMp9/7FTKUncp7fH9IwPfw+ysMObcEz5FWheQ=
 github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=
 github.com/olekukonko/tablewriter v0.0.5/go.mod h1:hPp6KlRPjbx+hW8ykQs1w3UBbZlj6HuIJcUGPhkA7kY=
 github.com/pingcap/errors v0.11.4 h1:lFuQV/oaUMGcD2tqt+01ROSmJs75VG1ToEOkZIZ4nE4=
@@ -57,6 +68,7 @@ github.com/rs/zerolog v1.28.0/go.mod h1:NILgTygv/Uej1ra5XxGf82ZFSLk58MFGAUS2o6us
 github.com/ssor/bom v0.0.0-20170718123548-6386211fdfcf h1:pvbZ0lM0XWPBqUKqFU8cmavspvIl9nulOYwdy6IFRRo=
 github.com/ssor/bom v0.0.0-20170718123548-6386211fdfcf/go.mod h1:RJID2RhlZKId02nZ62WenDCkgHFerpIOmW0iT7GKmXM=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
 github.com/tidwall/gjson v1.14.2/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
@@ -74,21 +86,28 @@ gitlab.com/etke.cc/go/env v1.0.0 h1:J98BwzOuELnjsVPFvz5wa79L7IoRV9CmrS41xLYXtSw=
 gitlab.com/etke.cc/go/env v1.0.0/go.mod h1:e1l4RM5MA1sc0R1w/RBDAESWRwgo5cOG9gx8BKUn2C4=
 gitlab.com/etke.cc/go/logger v1.1.0 h1:Yngp/DDLmJ0jJNLvLXrfan5Gi5QV+r7z6kCczTv8t4U=
 gitlab.com/etke.cc/go/logger v1.1.0/go.mod h1:8Vw5HFXlZQ5XeqvUs5zan+GnhrQyYtm/xe+yj8H/0zk=
+gitlab.com/etke.cc/go/secgen v1.1.0 h1:KFjFEXNlSPtY19ichNL+lQF2Q0vP3/9O2rVGZzVrqq0=
+gitlab.com/etke.cc/go/secgen v1.1.0/go.mod h1:3pJqRGeWApzx7qXjABqz2o2SMCNpKSZao/gXVdasqE8=
 gitlab.com/etke.cc/linkpearl v0.0.0-20220831124140-598117f26c77 h1:O9t4Sw/nu0JDUX+3KYjaqBi887opyNZ0imE+i2sV+q8=
 gitlab.com/etke.cc/linkpearl v0.0.0-20220831124140-598117f26c77/go.mod h1:CqwzwxVogKG6gDWTPTen3NyWbTESg42jxoTfXXwDGKQ=
+golang.org/x/crypto v0.0.0-20220518034528-6f7dac969898/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90 h1:Y/gsMcFOcR+6S6f3YeMKl5g+dZMEWqcz5Czj/GWYbkM=
 golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/net v0.0.0-20210501142056-aec3718b3fa0/go.mod h1:OJAsFXCWl8Ukc7SiCT/9KSuxbyM7479/AVlXFRxuMCk=
+golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.0.0-20220826154423-83b083e8dc8b h1:ZmngSVLe/wycRns9MKikG9OWIEjGcGAkacif7oYQaUY=
 golang.org/x/net v0.0.0-20220826154423-83b083e8dc8b/go.mod h1:YDH+HFinaLZZlnHAfSS6ZXJJ9M9t4Dl22yv3iI2vPwk=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220829200755-d48e67d00261 h1:v6hYoSR9T5oet+pMXwUWkbiVqx/63mlHjefrHmxwfeY=
 golang.org/x/sys v0.0.0-20220829200755-d48e67d00261/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.0.0-20210927222741-03fcf44c2211 h1:JGgROgKl9N8DuW20oFS5gxc+lE67/N3FcwmBPMe7ArY=
+golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
--- a/smtp/server.go
+++ b/smtp/server.go
@@ -10,40 +10,42 @@ import (
 	"gitlab.com/etke.cc/go/logger"
 )

-type backend struct {
+// msa is mail submission agent, implements smtp.Backend
+type msa struct {
 	log    *logger.Logger
 	domain string
-	client Client
+	bot    Bot
 }

-func (b *backend) newSession() *session {
-	return &session{
+func (m *msa) newSession() *msasession {
+	return &msasession{
 		ctx:    sentry.SetHubOnContext(context.Background(), sentry.CurrentHub().Clone()),
-		log:    b.log,
-		domain: b.domain,
-		client: b.client,
+		log:    m.log,
+		bot:    m.bot,
+		domain: m.domain,
 	}
 }

-func (b *backend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
+func (m *msa) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
 	return nil, smtp.ErrAuthUnsupported
 }

-func (b *backend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
-	return b.newSession(), nil
+func (m *msa) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
+	return m.newSession(), nil
 }

-func Start(domain, port, loglevel string, maxSize int, client Client) error {
+func Start(domain, port, loglevel string, maxSize int, bot Bot) error {
 	log := logger.New("smtp.", loglevel)
-	be := &backend{
+	sender := NewMTA(loglevel)
+	receiver := &msa{
 		log:    log,
+		bot:    bot,
 		domain: domain,
-		client: client,
 	}
-	s := smtp.NewServer(be)
+	receiver.bot.SetMTA(sender)
+	s := smtp.NewServer(receiver)
 	s.Addr = ":" + port
 	s.Domain = domain
-	s.AuthDisabled = true
 	s.ReadTimeout = 10 * time.Second
 	s.WriteTimeout = 10 * time.Second
 	s.MaxMessageBytes = maxSize * 1024 * 1024
--- a/smtp/msasession.go
+++ b/smtp/msasession.go
@@ -12,24 +12,24 @@ import (
 	"gitlab.com/etke.cc/postmoogle/utils"
 )

-type session struct {
+type msasession struct {
 	log    *logger.Logger
+	bot    Bot
 	domain string
-	client Client

 	ctx  context.Context
 	to   string
 	from string
 }

-func (s *session) Mail(from string, opts smtp.MailOptions) error {
+func (s *msasession) Mail(from string, opts smtp.MailOptions) error {
 	sentry.GetHubFromContext(s.ctx).Scope().SetTag("from", from)
 	s.from = from
 	s.log.Debug("mail from %s, options: %+v", from, opts)
 	return nil
 }

-func (s *session) Rcpt(to string) error {
+func (s *msasession) Rcpt(to string) error {
 	sentry.GetHubFromContext(s.ctx).Scope().SetTag("to", to)

 	if utils.Hostname(to) != s.domain {
@@ -37,7 +37,7 @@ func (s *session) Rcpt(to string) error {
 		return smtp.ErrAuthRequired
 	}

-	_, ok := s.client.GetMapping(utils.Mailbox(to))
+	_, ok := s.bot.GetMapping(utils.Mailbox(to))
 	if !ok {
 		s.log.Debug("mapping for %s not found", to)
 		return smtp.ErrAuthRequired
@@ -48,7 +48,7 @@ func (s *session) Rcpt(to string) error {
 	return nil
 }

-func (s *session) parseAttachments(parts []*enmime.Part) []*utils.File {
+func (s *msasession) parseAttachments(parts []*enmime.Part) []*utils.File {
 	files := make([]*utils.File, 0, len(parts))
 	for _, attachment := range parts {
 		for _, err := range attachment.Errors {
@@ -61,7 +61,7 @@ func (s *session) parseAttachments(parts []*enmime.Part) []*utils.File {
 	return files
 }

-func (s *session) Data(r io.Reader) error {
+func (s *msasession) Data(r io.Reader) error {
 	parser := enmime.NewParser()
 	eml, err := parser.ReadEnvelope(r)
 	if err != nil {
@@ -84,11 +84,11 @@ func (s *session) Data(r io.Reader) error {
 		eml.HTML,
 		files)

-	return s.client.Send(s.ctx, email)
+	return s.bot.Send2Matrix(s.ctx, email)
 }

-func (s *session) Reset() {}
+func (s *msasession) Reset() {}

-func (s *session) Logout() error {
+func (s *msasession) Logout() error {
 	return nil
 }
--- a/smtp/mta.go
+++ b/smtp/mta.go
@@ -0,0 +1,125 @@
+package smtp
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net"
+	"net/smtp"
+	"strings"
+
+	"gitlab.com/etke.cc/go/logger"
+	"maunium.net/go/mautrix/id"
+
+	"gitlab.com/etke.cc/postmoogle/utils"
+)
+
+// Bot interface to send emails into matrix
+type Bot interface {
+	GetMapping(string) (id.RoomID, bool)
+	Send2Matrix(ctx context.Context, email *utils.Email) error
+	SetMTA(mta utils.MTA)
+}
+
+// mta is Mail Transfer Agent
+type mta struct {
+	log *logger.Logger
+}
+
+func NewMTA(loglevel string) utils.MTA {
+	return &mta{
+		log: logger.New("smtp/mta.", loglevel),
+	}
+}
+
+func (m *mta) Send(from, to, data string) error {
+	m.log.Debug("Sending email from %s to %s", from, to)
+	conn, err := m.connect(from, to)
+	if err != nil {
+		m.log.Error("cannot connect to SMTP server of %s: %v", to, err)
+		return err
+	}
+	defer conn.Close()
+	err = conn.Mail(from)
+	if err != nil {
+		m.log.Error("cannot call MAIL command: %v", err)
+		return err
+	}
+	err = conn.Rcpt(to)
+	if err != nil {
+		m.log.Error("cannot send RCPT command: %v", err)
+		return err
+	}
+
+	var w io.WriteCloser
+	w, err = conn.Data()
+	if err != nil {
+		m.log.Error("cannot send DATA command: %v", err)
+		return err
+	}
+	defer w.Close()
+	m.log.Debug("sending DATA:\n%s", data)
+	_, err = strings.NewReader(data).WriteTo(w)
+	if err != nil {
+		m.log.Debug("cannot write DATA: %v", err)
+		return err
+	}
+
+	m.log.Debug("email has been sent")
+	return nil
+}
+
+func (m *mta) tryServer(localname, mxhost string) *smtp.Client {
+	m.log.Debug("trying SMTP connection to %s", mxhost)
+	conn, err := smtp.Dial(mxhost + ":smtp")
+	if err != nil {
+		m.log.Warn("cannot connect to the %s: %v", mxhost, err)
+		return nil
+	}
+	err = conn.Hello(localname)
+	if err != nil {
+		m.log.Warn("cannot call HELLO command of the %s: %v", mxhost, err)
+		return nil
+	}
+	if ok, _ := conn.Extension("STARTTLS"); ok {
+		m.log.Debug("%s supports STARTTLS", mxhost)
+		config := &tls.Config{ServerName: mxhost}
+		err = conn.StartTLS(config)
+		if err != nil {
+			m.log.Warn("STARTTLS connection to the %s failed: %v", mxhost, err)
+		}
+	}
+
+	return conn
+}
+
+func (m *mta) connect(from, to string) (*smtp.Client, error) {
+	localname := strings.SplitN(from, "@", 2)[1]
+	hostname := strings.SplitN(to, "@", 2)[1]
+
+	m.log.Debug("performing MX lookup of %s", hostname)
+	mxs, err := net.LookupMX(hostname)
+	if err != nil {
+		m.log.Error("cannot perform MX lookup: %v", err)
+		return nil, err
+	}
+
+	for _, mx := range mxs {
+		client := m.tryServer(localname, mx.Host)
+		if client != nil {
+			return client, nil
+		}
+	}
+
+	// If there are no MX records, according to https://datatracker.ietf.org/doc/html/rfc5321#section-5.1,
+	// we're supposed to try talking directly to the host.
+	if len(mxs) == 0 {
+		client := m.tryServer(localname, hostname)
+		if client != nil {
+			return client, nil
+		}
+	}
+
+	return nil, fmt.Errorf("target SMTP server not found")
+}
--- a/smtp/smtp.go
+++ b/smtp/smtp.go
@@ -1,15 +0,0 @@
-package smtp
-
-import (
-	"context"
-
-	"maunium.net/go/mautrix/id"
-
-	"gitlab.com/etke.cc/postmoogle/utils"
-)
-
-// Client interface to send emails
-type Client interface {
-	GetMapping(string) (id.RoomID, bool)
-	Send(ctx context.Context, email *utils.Email) error
-}
--- a/utils/command.go
+++ b/utils/command.go
@@ -0,0 +1,25 @@
+package utils
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ErrInvalidArgs returned when a command's arguments are invalid
+var ErrInvalidArgs = fmt.Errorf("invalid arguments")
+
+// ParseSend parses "!pm send" command, returns to, subject, body, err
+func ParseSend(commandSlice []string) (string, string, string, error) {
+	if len(commandSlice) < 3 {
+		return "", "", "", ErrInvalidArgs
+	}
+
+	message := strings.Join(commandSlice, " ")
+	lines := strings.Split(message, "\n")
+	commandSlice = strings.Split(lines[0], " ")
+	to := commandSlice[1]
+	subject := lines[1]
+	body := strings.Join(lines[2:], "\n")
+
+	return to, subject, body, nil
+}
--- a/utils/email.go
+++ b/utils/email.go
@@ -1,7 +1,26 @@
 package utils

+import (
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
+	"strings"
+	"time"
+
+	"github.com/emersion/go-msgauth/dkim"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/format"
+	"maunium.net/go/mautrix/id"
+)
+
+// MTA is mail transfer agent
+type MTA interface {
+	Send(from, to, data string) error
+}
+
 // Email object
 type Email struct {
+	Date      string
 	MessageID string
 	InReplyTo string
 	From      string
@@ -12,9 +31,25 @@ type Email struct {
 	Files     []*File
 }

+// ContentOptions represents settings that specify how an email is to be converted to a Matrix message
+type ContentOptions struct {
+	// On/Off
+	Sender  bool
+	Subject bool
+	HTML    bool
+	Threads bool
+
+	// Keys
+	MessageIDKey string
+	InReplyToKey string
+	SubjectKey   string
+	FromKey      string
+}
+
 // NewEmail constructs Email object
 func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files []*File) *Email {
 	email := &Email{
+		Date:      time.Now().UTC().Format(time.RFC1123Z),
 		MessageID: messageID,
 		InReplyTo: inReplyTo,
 		From:      from,
@@ -35,3 +70,105 @@ func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files

 	return email
 }
+
+// Content converts the email object to a Matrix event content
+func (e *Email) Content(threadID id.EventID, options *ContentOptions) *event.Content {
+	var text strings.Builder
+	if options.Sender {
+		text.WriteString("From: ")
+		text.WriteString(e.From)
+		text.WriteString("\n\n")
+	}
+	if options.Subject {
+		text.WriteString("# ")
+		text.WriteString(e.Subject)
+		text.WriteString("\n\n")
+	}
+	if e.HTML != "" && options.HTML {
+		text.WriteString(format.HTMLToMarkdown(e.HTML))
+	} else {
+		text.WriteString(e.Text)
+	}
+
+	parsed := format.RenderMarkdown(text.String(), true, true)
+	parsed.RelatesTo = RelatesTo(options.Threads, threadID)
+
+	content := event.Content{
+		Raw: map[string]interface{}{
+			options.MessageIDKey: e.MessageID,
+			options.InReplyToKey: e.InReplyTo,
+			options.SubjectKey:   e.Subject,
+			options.FromKey:      e.From,
+		},
+		Parsed: parsed,
+	}
+	return &content
+}
+
+// Compose converts the email object to a string (to be used for delivery via SMTP) and possibly DKIM-signs it
+func (e *Email) Compose(privkey string) string {
+	var data strings.Builder
+
+	domain := strings.SplitN(e.From, "@", 2)[0]
+	data.WriteString("From: ")
+	data.WriteString(e.From)
+	data.WriteString("\r\n")
+
+	data.WriteString("To: ")
+	data.WriteString(e.To)
+	data.WriteString("\r\n")
+
+	data.WriteString("Message-Id: ")
+	data.WriteString(e.MessageID)
+	data.WriteString("\r\n")
+
+	data.WriteString("Date: ")
+	data.WriteString(e.Date)
+	data.WriteString("\r\n")
+
+	if e.InReplyTo != "" {
+		data.WriteString("In-Reply-To: ")
+		data.WriteString(e.InReplyTo)
+		data.WriteString("\r\n")
+	}
+
+	data.WriteString("Subject: ")
+	data.WriteString(e.Subject)
+	data.WriteString("\r\n")
+
+	data.WriteString("\r\n")
+
+	data.WriteString(e.Text)
+	data.WriteString("\r\n")
+
+	return e.sign(domain, privkey, data)
+}
+
+func (e *Email) sign(domain, privkey string, data strings.Builder) string {
+	if privkey == "" {
+		return data.String()
+	}
+	pemblock, _ := pem.Decode([]byte(privkey))
+	if pemblock == nil {
+		return data.String()
+	}
+	parsedkey, err := x509.ParsePKCS8PrivateKey(pemblock.Bytes)
+	if err != nil {
+		return data.String()
+	}
+	signer := parsedkey.(crypto.Signer)
+
+	options := &dkim.SignOptions{
+		Domain:   domain,
+		Selector: "postmoogle",
+		Signer:   signer,
+	}
+
+	var msg strings.Builder
+	err = dkim.Sign(&msg, strings.NewReader(data.String()), options)
+	if err != nil {
+		return data.String()
+	}
+
+	return msg.String()
+}
--- a/utils/matrix.go
+++ b/utils/matrix.go
@@ -6,26 +6,65 @@ import (
 	"maunium.net/go/mautrix/id"
 )

-// RelatesTo block of matrix event content
-func RelatesTo(noThreads bool, parentID id.EventID) *event.RelatesTo {
+// RelatesTo returns relation object of a matrix event (either threads or reply-to)
+func RelatesTo(threads bool, parentID id.EventID) *event.RelatesTo {
 	if parentID == "" {
 		return nil
 	}

-	if noThreads {
+	if threads {
 		return &event.RelatesTo{
-			InReplyTo: &event.InReplyTo{
-				EventID: parentID,
-			},
+			Type:    event.RelThread,
+			EventID: parentID,
 		}
 	}

 	return &event.RelatesTo{
-		Type:    event.RelThread,
-		EventID: parentID,
+		InReplyTo: &event.InReplyTo{
+			EventID: parentID,
+		},
 	}
 }

+// EventParent returns parent event ID (either from thread or from reply-to relation)
+func EventParent(currentID id.EventID, content *event.MessageEventContent) id.EventID {
+	if content == nil {
+		return currentID
+	}
+
+	if content.GetRelatesTo() == nil {
+		return currentID
+	}
+
+	threadParent := content.RelatesTo.GetThreadParent()
+	if threadParent != "" {
+		return threadParent
+	}
+
+	replyParent := content.RelatesTo.GetReplyTo()
+	if replyParent != "" {
+		return replyParent
+	}
+
+	return currentID
+}
+
+// EventField returns field value from raw event content
+func EventField[T comparable](content *event.Content, field string) T {
+	var zero T
+	raw := content.Raw[field]
+	if raw == nil {
+		return zero
+	}
+
+	v, ok := raw.(T)
+	if !ok {
+		return zero
+	}
+
+	return v
+}
+
 // UnwrapError tries to unwrap a error into something meaningful, like mautrix.HTTPError or mautrix.RespError
 func UnwrapError(err error) error {
 	switch err.(type) {