dkim

bot/command.go

@@ -15,6 +15,7 @@ const (
 	commandHelp      = "help"
 	commandStop      = "stop"
 	commandSend      = "send"
+	commandDKIM      = "dkim"
 	commandUsers     = botOptionUsers
 	commandDelete    = "delete"
 	commandMailboxes = "mailboxes"
@@ -132,6 +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",
@@ -163,6 +169,8 @@ func (b *Bot) handleCommand(ctx context.Context, evt *event.Event, commandSlice
 		b.runStop(ctx)
 	case commandSend:
 		b.runSend(ctx, commandSlice)
+	case commandDKIM:
+		b.runDKIM(ctx)
 	case commandUsers:
 		b.runUsers(ctx, commandSlice)
 	case commandDelete:
@@ -272,7 +280,6 @@ func (b *Bot) runSend(ctx context.Context, commandSlice []string) {
 	subject := lines[1]
 	body := strings.Join(lines[2:], "\n")
 
-	b.log.Debug("to=%s subject=%s body=%s", to, subject, body)
 	err := b.Send2Email(ctx, to, subject, body)
 	if err != nil {
 		b.Error(ctx, evt.RoomID, "cannot send email: %v", err)

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))
+}

bot/email.go

@@ -2,11 +2,15 @@ package bot
 
 import (
 	"context"
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
 	"errors"
 	"fmt"
 	"strings"
 	"time"
 
+	"github.com/emersion/go-msgauth/dkim"
 	"maunium.net/go/mautrix/event"
 	"maunium.net/go/mautrix/format"
 	"maunium.net/go/mautrix/id"
@@ -234,9 +238,45 @@ func (b *Bot) Send2Email(ctx context.Context, to, subject, body string) error {
 	msg.WriteString(body)
 	msg.WriteString("\r\n")
 
+	msg = b.signDKIM(msg)
+
 	return b.mta.Send(from, to, msg.String())
 }
 
+func (b *Bot) signDKIM(body strings.Builder) strings.Builder {
+	privkey := b.getBotSettings().DKIMPrivateKey()
+	if privkey == "" {
+		b.log.Warn("DKIM private key not found, email will be sent unsigned")
+		return body
+	}
+	pemblock, _ := pem.Decode([]byte(privkey))
+	if pemblock == nil {
+		b.log.Error("cannot decode DKIM private key")
+		return body
+	}
+	parsedkey, err := x509.ParsePKCS8PrivateKey(pemblock.Bytes)
+	if err != nil {
+		b.log.Error("cannot parse PKCS8 private key: %v", err)
+		return body
+	}
+	signer := parsedkey.(crypto.Signer)
+
+	options := &dkim.SignOptions{
+		Domain:   b.domain,
+		Selector: "postmoogle",
+		Signer:   signer,
+	}
+
+	var msg strings.Builder
+	err = dkim.Sign(&msg, strings.NewReader(body.String()), options)
+	if err != nil {
+		b.log.Error("cannot sign email: %v", err)
+		return body
+	}
+
+	return msg
+}
+
 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()

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()