Add settings to allow different SMTP envelope from address (#17479)

* Add settings to allow different SMTP envelope from address

Sometimes it may be advisable to hide or alias the from address on an SMTP mail
envelope. This PR adds two new options to the mailer to allow setting of an overriding
from address.

Fix #17477

Signed-off-by: Andrew Thornton <art27@cantab.net>

custom/conf/app.example.ini

@@ -1457,6 +1457,9 @@ PATH =
 ;; Mail from address, RFC 5322. This can be just an email address, or the `"Name" <email@example.com>` format
 ;FROM =
 ;;
+;; Sometimes it is helpful to use a different address on the envelope. Set this to use ENVELOPE_FROM as the from on the envelope. Set to `<>` to send an empty address.
+;ENVELOPE_FROM =
+;;
 ;; Mailer user name and password
 ;; Please Note: Authentication is only supported when the SMTP server communication is encrypted with TLS (this can be via STARTTLS) or `HOST=localhost`.
 ;USER =

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -606,6 +606,7 @@ Define allowed algorithms and their minimum key length (use -1 to disable a type
   - Otherwise if `IS_TLS_ENABLED=false` and the server supports `STARTTLS` this will be used. Thus if `STARTTLS` is preferred you should set `IS_TLS_ENABLED=false`.
 - `FROM`: **\<empty\>**: Mail from address, RFC 5322. This can be just an email address, or
    the "Name" \<email@example.com\> format.
+- `ENVELOPE_FROM`: **\<empty\>**: Address set as the From address on the SMTP mail envelope. Set to `<>` to send an empty address.
 - `USER`: **\<empty\>**: Username of mailing user (usually the sender's e-mail address).
 - `PASSWD`: **\<empty\>**: Password of mailing user.  Use \`your password\` for quoting if you use special characters in the password.
    - Please note: authentication is only supported when the SMTP server communication is encrypted with TLS (this can be via `STARTTLS`) or `HOST=localhost`. See [Email Setup]({{< relref "doc/usage/email-setup.en-us.md" >}}) for more information.

modules/setting/mailer.go

@@ -18,6 +18,8 @@ type Mailer struct {
 	// Mailer
 	Name                 string
 	From                 string
+	EnvelopeFrom         string
+	OverrideEnvelopeFrom bool `ini:"-"`
 	FromName             string
 	FromEmail            string
 	SendAsPlainText      bool
@@ -73,6 +75,7 @@ func newMailService() {
 		SendmailTimeout: sec.Key("SENDMAIL_TIMEOUT").MustDuration(5 * time.Minute),
 	}
 	MailService.From = sec.Key("FROM").MustString(MailService.User)
+	MailService.EnvelopeFrom = sec.Key("ENVELOPE_FROM").MustString("")
 
 	if sec.HasKey("ENABLE_HTML_ALTERNATIVE") {
 		log.Warn("ENABLE_HTML_ALTERNATIVE is deprecated, use SEND_AS_PLAIN_TEXT")
@@ -93,6 +96,21 @@ func newMailService() {
 	MailService.FromName = parsed.Name
 	MailService.FromEmail = parsed.Address
 
+	switch MailService.EnvelopeFrom {
+	case "":
+		MailService.OverrideEnvelopeFrom = false
+	case "<>":
+		MailService.EnvelopeFrom = ""
+		MailService.OverrideEnvelopeFrom = true
+	default:
+		parsed, err = mail.ParseAddress(MailService.EnvelopeFrom)
+		if err != nil {
+			log.Fatal("Invalid mailer.ENVELOPE_FROM (%s): %v", MailService.EnvelopeFrom, err)
+		}
+		MailService.OverrideEnvelopeFrom = true
+		MailService.EnvelopeFrom = parsed.Address
+	}
+
 	if MailService.MailerType == "" {
 		MailService.MailerType = "smtp"
 	}

services/mailer/mailer.go

@@ -210,9 +210,15 @@ func (s *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 		}
 	}
 
+	if opts.OverrideEnvelopeFrom {
+		if err = client.Mail(opts.EnvelopeFrom); err != nil {
+			return fmt.Errorf("Mail: %v", err)
+		}
+	} else {
 		if err = client.Mail(from); err != nil {
 			return fmt.Errorf("Mail: %v", err)
 		}
+	}
 
 	for _, rec := range to {
 		if err = client.Rcpt(rec); err != nil {
@@ -242,7 +248,12 @@ func (s *sendmailSender) Send(from string, to []string, msg io.WriterTo) error {
 	var closeError error
 	var waitError error
 
-	args := []string{"-f", from, "-i"}
+	envelopeFrom := from
+	if setting.MailService.OverrideEnvelopeFrom {
+		envelopeFrom = setting.MailService.EnvelopeFrom
+	}
+
+	args := []string{"-f", envelopeFrom, "-i"}
 	args = append(args, setting.MailService.SendmailArgs...)
 	args = append(args, to...)
 	log.Trace("Sending with: %s %v", setting.MailService.SendmailPath, args)