feat: support setting custom sender domain (#79)

* feat: support setting custom sender domain

Some SMTP servers, such as the Gmail SMTP-relay, requires a proper
domain name in the inital EHLO/HELO exchange and will reject attempts to
use localhost.

* ci: replace deprecated linters

Switch deprecated linters to their suggested replacements.

* fix: handle HELO errors when using localname

Check the return value of the HELO when specifying a sender domain name.

---------

Co-authored-by: Dom Dwyer <[email protected]>

.golangci.yml

@@ -27,13 +27,13 @@ output:
 
 linters:
   enable:
-    - golint
+    - revive
     - gosec
     - unconvert
     - gocyclo
     - goimports
     - nakedret
-    - scopelint
+    - exportloopref
     - exhaustive
     - exportloopref
 

mailyak.go

@@ -16,6 +16,7 @@ type MailYak struct {
 	html  BodyPart
 	plain BodyPart
 
+	localName      string
 	toAddrs        []string
 	ccAddrs        []string
 	bccAddrs       []string
@@ -170,6 +171,12 @@ func (m *MailYak) Plain() *BodyPart {
 	return &m.plain
 }
 
+// getLocalName should return the sender domain to be used in the EHLO/HELO
+// command.
+func (m *MailYak) getLocalName() string {
+	return m.localName
+}
+
 // getToAddrs should return a slice of email addresses to be added to the
 // RCPT TO command.
 func (m *MailYak) getToAddrs() []string {

sender.go

@@ -16,6 +16,10 @@ type emailSender interface {
 
 // sendableMail provides a set of methods to describe an email to a SMTP server.
 type sendableMail interface {
+	// getLocalName should return the sender domain to be used in the EHLO/HELO
+	// command.
+	getLocalName() string
+
 	// getToAddrs should return a slice of email addresses to be added to the
 	// RCPT TO command.
 	getToAddrs() []string
@@ -46,6 +50,12 @@ func smtpExchange(m sendableMail, conn net.Conn, serverName string, tryTLSUpgrad
 	}
 	defer func() { _ = c.Quit() }()
 
+	if localName := m.getLocalName(); localName != "" {
+		if err := c.Hello(localName); err != nil {
+			return err
+		}
+	}
+
 	if tryTLSUpgrade {
 		if ok, _ := c.Extension("STARTTLS"); ok {
 			//nolint:gosec

sender_test.go

@@ -119,10 +119,17 @@ func newConnAsserts(c net.Conn, t *testing.T) *connAsserts {
 // mockMail provides the methods for a sendableMail, allowing for deterministic
 // MIME content in tests.
 type mockMail struct {
-	toAddrs  []string
-	fromAddr string
-	auth     smtp.Auth
-	mime     string
+	localName string
+	toAddrs   []string
+	fromAddr  string
+	auth      smtp.Auth
+	mime      string
+}
+
+// getLocalName should return the sender domain to be used in the EHLO/HELO
+// command.
+func (m *mockMail) getLocalName() string {
+	return m.localName
 }
 
 // toAddrs should return a slice of email addresses to be added to the RCPT
@@ -262,6 +269,48 @@ func TestSMTPProtocolExchange(t *testing.T) {
 			wantTLSErr:       nil,
 			wantPlaintextErr: nil,
 		},
+		{
+			name: "with localname",
+			mail: &mockMail{
+				toAddrs: []string{
+					"[email protected]",
+					"[email protected]",
+					"Dom <[email protected]>",
+				},
+				fromAddr:  "[email protected]",
+				mime:      "bananas",
+				localName: "example.com",
+			},
+			connFn: func(c *connAsserts) {
+				c.Respond("220 localhost ESMTP bananas\r\n")
+
+				c.Expect("EHLO example.com\r\n")
+				c.Respond("250-example.com Hola\r\n")
+				c.Respond("250 AUTH LOGIN PLAIN\r\n")
+
+				c.Expect("MAIL FROM:<[email protected]>\r\n")
+				c.Respond("250 OK\r\n")
+
+				c.Expect("RCPT TO:<[email protected]>\r\n")
+				c.Respond("250 OK\r\n")
+
+				c.Expect("RCPT TO:<[email protected]>\r\n")
+				c.Respond("250 OK\r\n")
+
+				c.Expect("RCPT TO:<[email protected]>\r\n")
+				c.Respond("250 OK\r\n")
+
+				c.Expect("DATA\r\n")
+				c.Respond("354 OK\r\n")
+				c.Expect("bananas\r\n.\r\n")
+				c.Respond("250 Will do friend\r\n")
+
+				c.Expect("QUIT\r\n")
+				c.Respond("221 Adios\r\n")
+			},
+			wantTLSErr:       nil,
+			wantPlaintextErr: nil,
+		},
 	}
 
 	// handleConn provides the accept loop for both the TLS server, and the
@@ -282,7 +331,7 @@ func TestSMTPProtocolExchange(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		var tt = tt
+		tt := tt
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 

setters.go

@@ -144,3 +144,13 @@ func (m *MailYak) Subject(sub string) {
 func (m *MailYak) AddHeader(name, value string) {
 	m.headers[m.trimRegex.ReplaceAllString(name, "")] = mime.QEncoding.Encode("UTF-8", m.trimRegex.ReplaceAllString(value, ""))
 }
+
+// LocalName sets the sender domain name.
+//
+// If set, it is used in the EHLO/HELO command instead of the default domain
+// (localhost, see [smtp.NewClient]). Some SMTP servers, such as the Gmail
+// SMTP-relay, requires a proper domain name and will reject attempts to use
+// localhost.
+func (m *MailYak) LocalName(name string) {
+	m.localName = m.trimRegex.ReplaceAllString(name, "")
+}

setters_test.go

@@ -301,3 +301,44 @@ func TestMailYakAddHeader(t *testing.T) {
 		})
 	}
 }
+
+func TestMailYakLocalName(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		// Test description.
+		name string
+		// Parameters.
+		from string
+		// Want
+		want string
+	}{
+		{
+			"empty",
+			"",
+			"",
+		},
+		{
+			"ASCII",
+			"example.com\r\n",
+			"example.com",
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			m := &MailYak{
+				headers:   map[string]string{},
+				trimRegex: regexp.MustCompile("\r?\n"),
+			}
+
+			m.LocalName(tt.from)
+
+			if !reflect.DeepEqual(m.localName, tt.want) {
+				t.Errorf("%q. MailYak.LocalName() = %v, want %v", tt.name, m.localName, tt.want)
+			}
+		})
+	}
+}