interpret Precedence: auto_reply as an auto reply (#7137)

Some email clients like to be special and only set the "Precedence" header to "auto_reply" when sending automatic replies.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7137
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: christopher-besch <mail@chris-besch.com>
Co-committed-by: christopher-besch <mail@chris-besch.com>

services/mailer/incoming/incoming.go

@@ -297,6 +297,10 @@ func isAutomaticReply(env *enmime.Envelope) bool {
 	if autoReply == "yes" {
 		return true
 	}
+	precedence := env.GetHeader("Precedence")
+	if precedence == "auto_reply" {
+		return true
+	}
 	autoRespond := env.GetHeader("X-Autorespond")
 	return autoRespond != ""
 }

services/mailer/incoming/incoming_test.go

@@ -65,6 +65,12 @@ func TestIsAutomaticReply(t *testing.T) {
 			},
 			Expected: true,
 		},
+		{
+			Headers: map[string]string{
+				"Precedence": "auto_reply",
+			},
+			Expected: true,
+		},
 	}
 
 	for _, c := range cases {