Added support for requesting MDNs as described in RFC 8098

README.md

@@ -43,6 +43,7 @@ Some of the features of this library:
 * [X] Support for attachments and inline embeds (from file system, `io.Reader` or `embed.FS`)
 * [X] Support for different encodings
 * [X] Support sending mails via a local sendmail command
+* [X] Support for requestng MDNs
 * [X] Message object satisfies `io.WriteTo` and `io.Reader` interfaces
 * [X] Support for Go's `html/template` and `text/template` (as message body, alternative part or attachment/emebed)
 * [X] Output to file support which allows storing mail messages as e. g. `.eml` files to disk to open them in a MUA

header.go

@@ -37,6 +37,10 @@ const (
 	// See: https://www.rfc-editor.org/rfc/rfc822#section-5.1
 	HeaderDate Header = "Date"
 
+	// HeaderDispositionNotificationTo is the MDN header as described in RFC8098
+	// See: https://www.rfc-editor.org/rfc/rfc8098.html#section-2.1
+	HeaderDispositionNotificationTo Header = "Disposition-Notification-To"
+
 	// HeaderImportance represents the "Importance" field
 	HeaderImportance Header = "Importance"
 

msg.go

@@ -37,6 +37,9 @@ const (
 
 	// errTplPointerNil is issued when a template pointer is expected but it is nil
 	errTplPointerNil = "template pointer is nil"
+
+	// errParseMailAddr is used when a mail address could not be validated
+	errParseMailAddr = "failed to parse mail address %q: %w"
 )
 
 // Msg is the mail message struct
@@ -175,7 +178,7 @@ func (m *Msg) SetAddrHeader(h AddrHeader, v ...string) error {
 	for _, av := range v {
 		a, err := mail.ParseAddress(av)
 		if err != nil {
-			return fmt.Errorf("failed to parse mail address header %q: %w", av, err)
+			return fmt.Errorf(errParseMailAddr, av, err)
 		}
 		al = append(al, a)
 	}
@@ -382,6 +385,51 @@ func (m *Msg) SetUserAgent(a string) {
 	m.SetHeader(HeaderXMailer, a)
 }
 
+// RequestMDNTo adds the Disposition-Notification-To header to request a MDN from the receiving end
+// as described in RFC8098. It allows to provide a list recipient addresses.
+// Address validation is performed
+// See: https://www.rfc-editor.org/rfc/rfc8098.html
+func (m *Msg) RequestMDNTo(t ...string) error {
+	var tl []string
+	for _, at := range t {
+		a, err := mail.ParseAddress(at)
+		if err != nil {
+			return fmt.Errorf(errParseMailAddr, at, err)
+		}
+		tl = append(tl, a.String())
+	}
+	m.genHeader[HeaderDispositionNotificationTo] = tl
+	return nil
+}
+
+// RequestMDNToFormat adds the Disposition-Notification-To header to request a MDN from the receiving end
+// as described in RFC8098. It allows to provide a recipient address with name and address and will format
+// accordingly. Address validation is performed
+// See: https://www.rfc-editor.org/rfc/rfc8098.html
+func (m *Msg) RequestMDNToFormat(n, a string) error {
+	return m.RequestMDNTo(fmt.Sprintf(`%s <%s>`, n, a))
+}
+
+// RequestMDNAddTo adds an additional recipient to the recipient list of the MDN
+func (m *Msg) RequestMDNAddTo(t string) error {
+	a, err := mail.ParseAddress(t)
+	if err != nil {
+		return fmt.Errorf(errParseMailAddr, t, err)
+	}
+	var tl []string
+	for _, cl := range m.genHeader[HeaderDispositionNotificationTo] {
+		tl = append(tl, cl)
+	}
+	tl = append(tl, a.String())
+	m.genHeader[HeaderDispositionNotificationTo] = tl
+	return nil
+}
+
+// RequestMDNAddToFormat adds an additional formated recipient to the recipient list of the MDN
+func (m *Msg) RequestMDNAddToFormat(n, a string) error {
+	return m.RequestMDNAddTo(fmt.Sprintf(`"%s" <%s>`, n, a))
+}
+
 // GetSender returns the currently set envelope FROM address. If no envelope FROM is set it will use
 // the first mail body FROM address. If ff is true, it will return the full address string including
 // the address name, if set

msg_test.go

@@ -927,6 +927,90 @@ func TestMsg_SetUserAgent(t *testing.T) {
 	}
 }
 
+// TestMsg_RequestMDN tests the different RequestMDN* related methods of Msg
+func TestMsg_RequestMDN(t *testing.T) {
+	n := "Toni Tester"
+	n2 := "Melanie Tester"
+	v := "toni.tester@example.com"
+	v2 := "melanie.tester@example.com"
+	iv := "testertest.tld"
+	vl := []string{v, v2}
+	m := NewMsg()
+
+	// Single valid address
+	if err := m.RequestMDNTo(v); err != nil {
+		t.Errorf("RequestMDNTo with a single valid address failed: %s", err)
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf("<%s>", v) {
+		t.Errorf("RequestMDNTo with a single valid address failed. Expected: %s, got: %s", v,
+			m.genHeader[HeaderDispositionNotificationTo][0])
+	}
+	m.Reset()
+
+	// Multiples valid addresses
+	if err := m.RequestMDNTo(vl...); err != nil {
+		t.Errorf("RequestMDNTo with a multiple valid address failed: %s", err)
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf("<%s>", v) {
+		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 0: %s, got 0: %s", v,
+			m.genHeader[HeaderDispositionNotificationTo][0])
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf("<%s>", v2) {
+		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
+			m.genHeader[HeaderDispositionNotificationTo][1])
+	}
+	m.Reset()
+
+	// Invalid address
+	if err := m.RequestMDNTo(iv); err == nil {
+		t.Errorf("RequestMDNTo with an invalid address was supposed to failed, but didn't")
+	}
+	m.Reset()
+
+	// Single valid addresses + AddTo
+	if err := m.RequestMDNTo(v); err != nil {
+		t.Errorf("RequestMDNTo with a single valid address failed: %s", err)
+	}
+	if err := m.RequestMDNAddTo(v2); err != nil {
+		t.Errorf("RequestMDNAddTo with a valid address failed: %s", err)
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf("<%s>", v2) {
+		t.Errorf("RequestMDNTo with a multiple valid addresses failed. Expected 1: %s, got 1: %s", v2,
+			m.genHeader[HeaderDispositionNotificationTo][1])
+	}
+	m.Reset()
+
+	// Single valid address formated + AddToFromat
+	if err := m.RequestMDNToFormat(n, v); err != nil {
+		t.Errorf("RequestMDNToFormat with a single valid address failed: %s", err)
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][0] != fmt.Sprintf(`"%s" <%s>`, n, v) {
+		t.Errorf(`RequestMDNToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n, v,
+			m.genHeader[HeaderDispositionNotificationTo][0])
+	}
+	if err := m.RequestMDNAddToFormat(n2, v2); err != nil {
+		t.Errorf("RequestMDNAddToFormat with a valid address failed: %s", err)
+	}
+	if m.genHeader[HeaderDispositionNotificationTo][1] != fmt.Sprintf(`"%s" <%s>`, n2, v2) {
+		t.Errorf(`RequestMDNAddToFormat with a single valid address failed. Expected: "%s" <%s>, got: %s`, n2, v2,
+			m.genHeader[HeaderDispositionNotificationTo][1])
+	}
+	m.Reset()
+
+	// Invalid formated address
+	if err := m.RequestMDNToFormat(n, iv); err == nil {
+		t.Errorf("RequestMDNToFormat with an invalid address was supposed to failed, but didn't")
+	}
+
+	// Invalid address AddTo + AddToFormat
+	if err := m.RequestMDNAddTo(iv); err == nil {
+		t.Errorf("RequestMDNAddTo with an invalid address was supposed to failed, but didn't")
+	}
+	if err := m.RequestMDNAddToFormat(n, iv); err == nil {
+		t.Errorf("RequestMDNAddToFormat with an invalid address was supposed to failed, but didn't")
+	}
+}
+
 // TestMsg_SetBodyString tests the Msg.SetBodyString method
 func TestMsg_SetBodyString(t *testing.T) {
 	tests := []struct {