dkim

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()