From 8b2ec4b02a98bfa32f80c7bac8df89120cb424d4 Mon Sep 17 00:00:00 2001
From: Robert Sesek <rsesek@bluestatic.org>
Date: Mon, 9 Mar 2026 00:14:51 -0400
Subject: [PATCH] Refactor mta.RelayFailure into CreateFailureEnvelope

---
 smtp/relay.go | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/smtp/relay.go b/smtp/relay.go
index b99230c..7ab3ab1 100644
--- a/smtp/relay.go
+++ b/smtp/relay.go
@@ -39,14 +39,29 @@ type mta struct {
 // information about the attempted delivery.
 func (m *mta) RelayFailure(env Envelope, log *zap.Logger, to, errorStr string, sendErr error) {
 	log.Error(errorStr, zap.Error(sendErr))
+	env, err := CreateFailureEnvelope(env, to, errorStr, sendErr)
+	if err != nil {
+		log.Error("Failed to prepare failure envelope", zap.Error(err))
+		return
+	}
+	m.server.DeliverMessage(env)
+}
 
+// CreateFailureEnvelope takes the message `env` and produces a delivery failure
+// notification message that wraps it. `errorStr` is reported to the sender in the
+// message. The `to` string identifies the specific recipient, if the envelope is
+// addressed to more than one.
+func CreateFailureEnvelope(env Envelope, to, errorStr string, sendErr error) (Envelope, error) {
 	buf := &bytes.Buffer{}
 	mw := multipart.NewWriter(buf)
 
 	now := time.Now()
 
 	failure := Envelope{
-		MailFrom: mail.Address{"mailpopbox", "mailbox@" + DomainForAddress(env.MailFrom)},
+		MailFrom: mail.Address{
+			Name:    "mailpopbox",
+			Address: "mailbox@" + DomainForAddress(env.MailFrom),
+		},
 		RcptTo:   []mail.Address{env.MailFrom},
 		ID:       generateEnvelopeId("f", now),
 		Received: now,
@@ -64,8 +79,7 @@ func (m *mta) RelayFailure(env Envelope, log *zap.Logger, to, errorStr string, s
 		"Content-Type": []string{"text/plain; charset=UTF-8"},
 	})
 	if err != nil {
-		log.Error("failed to create multipart 0", zap.Error(err))
-		return
+		return Envelope{}, fmt.Errorf("failed to create multipart 0: %w", err)
 	}
 	fmt.Fprintf(tw, "* * * Delivery Failure * * *\n\n")
 	fmt.Fprintf(tw, "The server failed to relay the message:\n\n%s:\n%s\n", errorStr, sendErr.Error())
@@ -74,8 +88,7 @@ func (m *mta) RelayFailure(env Envelope, log *zap.Logger, to, errorStr string, s
 		"Content-Type": []string{"message/delivery-status"},
 	})
 	if err != nil {
-		log.Error("failed to create multipart 1", zap.Error(err))
-		return
+		return Envelope{}, fmt.Errorf("failed to create multipart 1: %w", err)
 	}
 	fmt.Fprintf(sw, "Original-Envelope-ID: %s\n", env.ID)
 	fmt.Fprintf(sw, "Reporting-UA: %s\n", env.EHLO)
@@ -88,8 +101,7 @@ func (m *mta) RelayFailure(env Envelope, log *zap.Logger, to, errorStr string, s
 		"Content-Type": []string{"message/rfc822"},
 	})
 	if err != nil {
-		log.Error("failed to create multipart 2", zap.Error(err))
-		return
+		return Envelope{}, fmt.Errorf("failed to create multipart 2: %w", err)
 	}
 
 	ocw.Write(env.Data)
@@ -97,5 +109,5 @@ func (m *mta) RelayFailure(env Envelope, log *zap.Logger, to, errorStr string, s
 	mw.Close()
 
 	failure.Data = buf.Bytes()
-	m.server.DeliverMessage(failure)
+	return failure, nil
 }
-- 
2.52.0