From 7881935f54b02d00cd61960e1908c0e8e5b12e93 Mon Sep 17 00:00:00 2001
From: dajiaohuang <108231307+dajiaohuang@users.noreply.github.com>
Date: Fri, 16 Oct 2026 18:33:25 +0800
Subject: [PATCH] Fix IPv6 remote address formatting

---
 remotes.go      |  3 +-
 remotes_test.go | 20 +++++++++++
 smtp_test.go    | 88 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 110 insertions(+), 1 deletion(-)
 create mode 100644 smtp_test.go

diff --git a/remotes.go b/remotes.go
index 486bef5..5e5783a 100644
--- a/remotes.go
+++ b/remotes.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"net"
 	"net/smtp"
 	"net/url"
 )
@@ -55,7 +56,7 @@ func ParseRemote(remoteURL string) (*Remote, error) {
 		Scheme:   u.Scheme,
 		Hostname: hostname,
 		Port:     port,
-		Addr:     fmt.Sprintf("%s:%s", hostname, port),
+		Addr:     net.JoinHostPort(hostname, port),
 	}
 
 	if u.User != nil {
diff --git a/remotes_test.go b/remotes_test.go
index 74ca960..0d11fe0 100644
--- a/remotes_test.go
+++ b/remotes_test.go
@@ -107,6 +107,26 @@ func TestValidRemoteUrls(t *testing.T) {
 	}, "starttls://user:pass@email.com:8425/sender@website.com?auth=login&skipVerify")
 }
 
+func TestIPv6RemoteUrls(t *testing.T) {
+	for _, test := range []struct {
+		url, scheme, port string
+	}{
+		{"smtp://[::1]", "smtp", "25"},
+		{"smtps://[::1]", "smtps", "465"},
+		{"starttls://[::1]", "starttls", "587"},
+		{"smtp://[::1]:2525", "smtp", "2525"},
+	} {
+		t.Run(test.url, func(t *testing.T) {
+			AssertRemoteUrlEquals(t, &Remote{
+				Scheme:   test.scheme,
+				Hostname: "::1",
+				Port:     test.port,
+				Addr:     "[::1]:" + test.port,
+			}, test.url)
+		})
+	}
+}
+
 func TestMissingScheme(t *testing.T) {
 	_, err := ParseRemote("http://user:pass@email.com:8425/sender@website.com")
 	assert.NotNil(t, err, "Err must be present")
diff --git a/smtp_test.go b/smtp_test.go
new file mode 100644
index 0000000..0249199
--- /dev/null
+++ b/smtp_test.go
@@ -0,0 +1,88 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"net/textproto"
+	"testing"
+	"time"
+)
+
+func TestSendMailIPv6Remote(t *testing.T) {
+	listener, err := net.Listen("tcp6", "[::1]:0")
+	if err != nil {
+		t.Skipf("IPv6 loopback unavailable: %v", err)
+	}
+	defer listener.Close()
+	if err := listener.(*net.TCPListener).SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
+		t.Fatal(err)
+	}
+
+	result := make(chan error, 1)
+	go func() {
+		result <- serveTestSMTP(listener)
+	}()
+
+	remote, err := ParseRemote("smtp://" + listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := SendMail(remote, "sender@example.invalid", []string{"recipient@example.invalid"}, []byte("Subject: loopback test\r\n\r\nsynthetic fixture\r\n")); err != nil {
+		t.Fatal(err)
+	}
+	if err := <-result; err != nil {
+		t.Fatal(err)
+	}
+}
+
+// This sink accepts only the synthetic transaction used above, never relaying it.
+func serveTestSMTP(listener net.Listener) error {
+	conn, err := listener.Accept()
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	if err := conn.SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
+		return err
+	}
+	text := textproto.NewConn(conn)
+	if err := text.PrintfLine("220 loopback test"); err != nil {
+		return err
+	}
+	commands := []struct{ command, response string }{
+		{"EHLO " + *hostName, "250 loopback test"},
+		{"MAIL FROM:<sender@example.invalid>", "250 OK"},
+		{"RCPT TO:<recipient@example.invalid>", "250 OK"},
+		{"DATA", "354 End with a dot"},
+	}
+	for _, step := range commands {
+		line, err := text.ReadLine()
+		if err != nil {
+			return err
+		}
+		if line != step.command {
+			return fmt.Errorf("command = %q, want %q", line, step.command)
+		}
+		if err := text.PrintfLine("%s", step.response); err != nil {
+			return err
+		}
+	}
+	data, err := text.ReadDotBytes()
+	if err != nil {
+		return err
+	}
+	if string(data) != "Subject: loopback test\n\nsynthetic fixture\n" {
+		return fmt.Errorf("unexpected DATA: %q", data)
+	}
+	if err := text.PrintfLine("250 OK"); err != nil {
+		return err
+	}
+	line, err := text.ReadLine()
+	if err != nil {
+		return err
+	}
+	if line != "QUIT" {
+		return fmt.Errorf("command = %q, want QUIT", line)
+	}
+	return text.PrintfLine("221 Bye")
+}