fix: send the bare address as SMTP envelope sender so mailcow DKIM-signs

mail/sender_test.go

@@ -11,9 +11,24 @@ import (
 	"testing"
 )
 
+// The envelope carries the bare address. "Vantage <x@y>" as MAIL FROM left
+// rspamd with no envelope sender, and mailcow skipped DKIM signing.
+func TestAddrSpecStripsDisplayName(t *testing.T) {
+	for in, want := range map[string]string{
+		"Vantage <support@example.com>": "support@example.com",
+		"support@example.com":           "support@example.com",
+		" a@example.com ":               "a@example.com",
+		"not an address":                "not an address",
+	} {
+		if got := addrSpec(in); got != want {
+			t.Errorf("addrSpec(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
 // Every part must declare quoted-printable and put only 7-bit bytes on the
 // wire. Raw UTF-8 under an implied 7bit encoding scored R_BAD_CTE_7BIT in
-// rspamd, went out without a DKIM signature, and landed in Gmail's spam.
+// rspamd.
 func TestEnvelopePartsAreQuotedPrintable(t *testing.T) {
 	s := Sender{From: "Vantage <support@example.com>"}
 	m := message{