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>

4 files changed, 43 insertions, 10 deletions

diff --git a/custom/conf/app.example.ini b/custom/conf/app.example.ini
index 9643e396b6..233e8981cb 100644
--- a/custom/conf/app.example.ini
+++ b/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 =
diff --git a/docs/content/doc/advanced/config-cheat-sheet.en-us.md b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
index a087b253e9..ae4f754170 100644
--- a/docs/content/doc/advanced/config-cheat-sheet.en-us.md
+++ b/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.
diff --git a/modules/setting/mailer.go b/modules/setting/mailer.go
index d2fac440ac..1bcd63a914 100644
--- a/modules/setting/mailer.go
+++ b/modules/setting/mailer.go
@@ -16,13 +16,15 @@ import (
 // Mailer represents mail service.
 type Mailer struct {
 	// Mailer
-	Name            string
-	From            string
-	FromName        string
-	FromEmail       string
-	SendAsPlainText bool
-	MailerType      string
-	SubjectPrefix   string
+	Name                 string
+	From                 string
+	EnvelopeFrom         string
+	OverrideEnvelopeFrom bool `ini:"-"`
+	FromName             string
+	FromEmail            string
+	SendAsPlainText      bool
+	MailerType           string
+	SubjectPrefix        string
 
 	// SMTP sender
 	Host              string
@@ -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"
 	}
diff --git a/services/mailer/mailer.go b/services/mailer/mailer.go
index fae8d473e3..0c0c626627 100644
--- a/services/mailer/mailer.go
+++ b/services/mailer/mailer.go
@@ -210,8 +210,14 @@ func (s *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 		}
 	}
 
-	if err = client.Mail(from); err != nil {
-		return fmt.Errorf("Mail: %v", err)
+	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 {
@@ -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)