feat: add mail_v3 functionality for reply_to_list (#471)

Add reply_to_list functionality to mail send api

helpers/mail/mail_v3.go

@@ -37,6 +37,7 @@ type SGMailV3 struct {
 	MailSettings     *MailSettings      `json:"mail_settings,omitempty"`
 	TrackingSettings *TrackingSettings  `json:"tracking_settings,omitempty"`
 	ReplyTo          *Email             `json:"reply_to,omitempty"`
+	ReplyToList      []*Email           `json:"reply_to_list,omitempty"`
 }
 
 // Personalization holds mail body struct
@@ -232,6 +233,12 @@ func (s *SGMailV3) SetReplyTo(e *Email) *SGMailV3 {
 	return s
 }
 
+// SetReplyToList ...
+func (s *SGMailV3) SetReplyToList(e []*Email) *SGMailV3 {
+	s.ReplyToList = e
+	return s
+}
+
 // SetTemplateID ...
 func (s *SGMailV3) SetTemplateID(templateID string) *SGMailV3 {
 	s.TemplateID = templateID

helpers/mail/mail_v3_test.go

@@ -96,6 +96,17 @@ func TestV3SetReplyTo(t *testing.T) {
 	assert.Equal(t, address, m.ReplyTo.Address, fmt.Sprintf("address should be %s, got %s", address, e.Address))
 }
 
+func TestV3SetReplyToList(t *testing.T) {
+	m := NewV3Mail()
+	replyTos := []*Email{
+		NewEmail("Example User", "[email protected]"),
+		NewEmail("Example User", "[email protected]"),
+	}
+	m.SetReplyToList(replyTos)
+
+	assert.Equal(t, len(replyTos), len(m.ReplyToList), fmt.Sprintf("length of To should be %d, got %d", len(replyTos), len(m.ReplyToList)))
+}
+
 func TestV3SetTemplateID(t *testing.T) {
 	m := NewV3Mail()