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>

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"
 	}