use postmoogle as general purpose SMTP server and allow other apps or scripts to send emails through it

.gitignore

@@ -1,3 +1,4 @@
 /local.db
 /local.db-journal
 /cover.out
+/e2e/main.go

README.md

@@ -30,6 +30,7 @@ It can't be used with arbitrary email providers, but setup your own provider "wi
 ### Send
 
 - [x] SMTP client
+- [x] SMTP server (you can use Postmoogle as general purpose SMTP server to send emails from your scripts or apps)
 - [x] Send a message to matrix room with special format to send a new email
 - [ ] Reply to matrix thread sends reply into email thread
 
@@ -237,6 +238,7 @@ If you want to change them - check available options in the help message (`!pm h
 
 * **!pm mailbox** - Get or set mailbox of the room
 * **!pm owner** - Get or set owner of the room
+* **!pm password** - Get or set SMTP password of the room's mailbox
 
 ---
 

bot/access.go

@@ -65,3 +65,18 @@ func (b *Bot) allowSend(actorID id.UserID, targetRoomID id.RoomID) bool {
 
 	return !cfg.NoSend()
 }
+
+// AllowAuth check if SMTP login (mailbox) and password are valid
+func (b *Bot) AllowAuth(mailbox, password string) bool {
+	roomID, ok := b.GetMapping(mailbox)
+	if !ok {
+		return false
+	}
+	cfg, err := b.getRoomSettings(roomID)
+	if err != nil {
+		b.log.Error("failed to retrieve settings: %v", err)
+		return false
+	}
+
+	return cfg.Password() != "" && cfg.Password() == password
+}

bot/command.go

@@ -73,6 +73,12 @@ func (b *Bot) initCommands() commandList {
 			sanitizer:   func(s string) string { return s },
 			allowed:     b.allowOwner,
 		},
+		{
+			key:         roomOptionPassword,
+			description: "Get or set SMTP password of the room's mailbox",
+			sanitizer:   func(s string) string { return strings.TrimSpace(s) },
+			allowed:     b.allowOwner,
+		},
 		{allowed: b.allowOwner}, // delimiter
 		{
 			key: roomOptionNoSend,
@@ -293,6 +299,11 @@ func (b *Bot) runSend(ctx context.Context) {
 		return
 	}
 
+	if !utils.AddressValid(to) {
+		b.Error(ctx, evt.RoomID, "email address is not valid")
+		return
+	}
+
 	cfg, err := b.getRoomSettings(evt.RoomID)
 	if err != nil {
 		b.Error(ctx, evt.RoomID, "failed to retrieve room settings: %v", err)

bot/email.go

@@ -46,8 +46,8 @@ func (b *Bot) GetMapping(mailbox string) (id.RoomID, bool) {
 }
 
 // Send email to matrix room
-func (b *Bot) Send2Matrix(ctx context.Context, email *utils.Email) error {
+func (b *Bot) Send2Matrix(ctx context.Context, email *utils.Email, local bool) error {
-	roomID, ok := b.GetMapping(utils.Mailbox(email.To))
+	roomID, ok := b.GetMapping(email.Mailbox(local))
 	if !ok {
 		return errors.New("room not found")
 	}
@@ -59,6 +59,10 @@ func (b *Bot) Send2Matrix(ctx context.Context, email *utils.Email) error {
 		b.Error(ctx, roomID, "cannot get settings: %v", err)
 	}
 
+	if !local && cfg.NoSend() {
+		return errors.New("that mailbox is receive-only")
+	}
+
 	var threadID id.EventID
 	if email.InReplyTo != "" && !cfg.NoThreads() {
 		threadID = b.getThreadID(roomID, email.InReplyTo)
@@ -81,6 +85,11 @@ func (b *Bot) Send2Matrix(ctx context.Context, email *utils.Email) error {
 	if !cfg.NoFiles() {
 		b.sendFiles(ctx, roomID, email.Files, cfg.NoThreads(), threadID)
 	}
+
+	if !local {
+		email.MessageID = fmt.Sprintf("<%s@%s>", eventID, b.domain)
+		return b.mta.Send(email.From, email.To, email.Compose(b.getBotSettings().DKIMPrivateKey()))
+	}
 	return nil
 }
 

bot/settings_room.go

@@ -21,6 +21,7 @@ const (
 	roomOptionNoHTML    = "nohtml"
 	roomOptionNoThreads = "nothreads"
 	roomOptionNoFiles   = "nofiles"
+	roomOptionPassword  = "password"
 )
 
 type roomSettings map[string]string
@@ -43,6 +44,10 @@ func (s roomSettings) Owner() string {
 	return s.Get(roomOptionOwner)
 }
 
+func (s roomSettings) Password() string {
+	return s.Get(roomOptionPassword)
+}
+
 func (s roomSettings) NoSend() bool {
 	return utils.Bool(s.Get(roomOptionNoSend))
 }

smtp/msa.go

@@ -2,10 +2,13 @@ package smtp
 
 import (
 	"context"
+	"errors"
 
 	"github.com/emersion/go-smtp"
 	"github.com/getsentry/sentry-go"
 	"gitlab.com/etke.cc/go/logger"
+
+	"gitlab.com/etke.cc/postmoogle/utils"
 )
 
 // msa is mail submission agent, implements smtp.Backend
@@ -13,11 +16,15 @@ type msa struct {
 	log    *logger.Logger
 	domain string
 	bot    Bot
+	mta    utils.MTA
 }
 
-func (m *msa) newSession() *msasession {
+func (m *msa) newSession(from string, local bool) *msasession {
 	return &msasession{
 		ctx:    sentry.SetHubOnContext(context.Background(), sentry.CurrentHub().Clone()),
+		mta:    m.mta,
+		from:   from,
+		local:  local,
 		log:    m.log,
 		bot:    m.bot,
 		domain: m.domain,
@@ -25,9 +32,18 @@ func (m *msa) newSession() *msasession {
 }
 
 func (m *msa) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
-	return nil, smtp.ErrAuthUnsupported
+	if !utils.AddressValid(username) {
+		return nil, errors.New("please, provide email address")
+	}
+
+	mailbox := utils.Mailbox(username)
+	if !m.bot.AllowAuth(mailbox, password) {
+		return nil, errors.New("email or password is invalid")
+	}
+
+	return m.newSession(username, false), nil
 }
 
 func (m *msa) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
-	return m.newSession(), nil
+	return m.newSession("", true), nil
 }

smtp/msasession.go

@@ -2,6 +2,7 @@ package smtp
 
 import (
 	"context"
+	"errors"
 	"io"
 
 	"github.com/emersion/go-smtp"
@@ -15,32 +16,41 @@ import (
 type msasession struct {
 	log    *logger.Logger
 	bot    Bot
+	mta    utils.MTA
 	domain string
 
-	ctx  context.Context
+	ctx   context.Context
-	to   string
+	local bool
-	from string
+	to    string
+	from  string
 }
 
 func (s *msasession) Mail(from string, opts smtp.MailOptions) error {
 	sentry.GetHubFromContext(s.ctx).Scope().SetTag("from", from)
-	s.from = from
+	if !utils.AddressValid(from) {
-	s.log.Debug("mail from %s, options: %+v", from, opts)
+		return errors.New("please, provide email address")
+	}
+	if s.local {
+		s.from = from
+		s.log.Debug("mail from %s, options: %+v", from, opts)
+	}
 	return nil
 }
 
 func (s *msasession) Rcpt(to string) error {
 	sentry.GetHubFromContext(s.ctx).Scope().SetTag("to", to)
 
-	if utils.Hostname(to) != s.domain {
+	if s.local {
-		s.log.Debug("wrong domain of %s", to)
+		if utils.Hostname(to) != s.domain {
-		return smtp.ErrAuthRequired
+			s.log.Debug("wrong domain of %s", to)
-	}
+			return smtp.ErrAuthRequired
+		}
 
-	_, ok := s.bot.GetMapping(utils.Mailbox(to))
+		_, ok := s.bot.GetMapping(utils.Mailbox(to))
-	if !ok {
+		if !ok {
-		s.log.Debug("mapping for %s not found", to)
+			s.log.Debug("mapping for %s not found", to)
-		return smtp.ErrAuthRequired
+			return smtp.ErrAuthRequired
+		}
 	}
 
 	s.to = to
@@ -80,7 +90,7 @@ func (s *msasession) Data(r io.Reader) error {
 		eml.HTML,
 		files)
 
-	return s.bot.Send2Matrix(s.ctx, email)
+	return s.bot.Send2Matrix(s.ctx, email, s.local)
 }
 
 func (s *msasession) Reset() {}

smtp/mta.go

@@ -17,8 +17,9 @@ import (
 
 // Bot interface to send emails into matrix
 type Bot interface {
+	AllowAuth(string, string) bool
 	GetMapping(string) (id.RoomID, bool)
-	Send2Matrix(ctx context.Context, email *utils.Email) error
+	Send2Matrix(ctx context.Context, email *utils.Email, local bool) error
 	SetMTA(mta utils.MTA)
 }
 

smtp/server.go

@@ -40,6 +40,7 @@ func NewServer(cfg *Config) *Server {
 	sender := NewMTA(cfg.LogLevel)
 	receiver := &msa{
 		log:    log,
+		mta:    sender,
 		bot:    cfg.Bot,
 		domain: cfg.Domain,
 	}
@@ -51,6 +52,7 @@ func NewServer(cfg *Config) *Server {
 	s.WriteTimeout = 10 * time.Second
 	s.MaxMessageBytes = cfg.MaxSize * 1024 * 1024
 	s.EnableREQUIRETLS = cfg.TLSRequired
+	s.AllowInsecureAuth = !cfg.TLSRequired
 	if log.GetLevel() == "DEBUG" || log.GetLevel() == "TRACE" {
 		s.Debug = os.Stdout
 	}

utils/email.go

@@ -4,6 +4,7 @@ import (
 	"crypto"
 	"crypto/x509"
 	"encoding/pem"
+	"regexp"
 	"strings"
 	"time"
 
@@ -13,6 +14,8 @@ import (
 	"maunium.net/go/mautrix/id"
 )
 
+var emailRegex = regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")
+
 // MTA is mail transfer agent
 type MTA interface {
 	Send(from, to, data string) error
@@ -46,6 +49,11 @@ type ContentOptions struct {
 	FromKey      string
 }
 
+// AddressValid checks if email address is valid
+func AddressValid(email string) bool {
+	return !emailRegex.MatchString(email)
+}
+
 // NewEmail constructs Email object
 func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files []*File) *Email {
 	email := &Email{
@@ -71,6 +79,14 @@ func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files
 	return email
 }
 
+// Mailbox returns postmoogle's mailbox, parsing it from FROM (if local=false) or TO (local=true)
+func (e *Email) Mailbox(local bool) string {
+	if local {
+		return Mailbox(e.To)
+	}
+	return Mailbox(e.From)
+}
+
 // 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