fix: include missing mail headers (resolve #472)

models/mail.go

@@ -2,18 +2,22 @@ package models
 
 import (
 	"fmt"
+	uuid "github.com/satori/go.uuid"
 	"strings"
+	"time"
 )
 
 const HtmlType = "text/html; charset=UTF-8"
 const PlainType = "text/html; charset=UTF-8"
 
 type Mail struct {
-	From    MailAddress
-	To      MailAddresses
-	Subject string
-	Body    string
-	Type    string
+	From      MailAddress
+	To        MailAddresses
+	Subject   string
+	Body      string
+	Type      string
+	Date      time.Time
+	MessageID string
 }
 
 func (m *Mail) WithText(text string) *Mail {
@@ -28,17 +32,36 @@ func (m *Mail) WithHTML(html string) *Mail {
 	return m
 }
 
+func (m *Mail) Sanitized() *Mail {
+	if m.Type == "" {
+		m.Type = PlainType
+	}
+	if m.Date.IsZero() {
+		m.Date = time.Now()
+	}
+	if m.MessageID == "" {
+		m.MessageID = fmt.Sprintf("<%s@%s>", uuid.NewV4().String(), m.From.Domain())
+	}
+	return m
+}
+
 func (m *Mail) String() string {
 	return fmt.Sprintf("To: %s\r\n"+
 		"From: %s\r\n"+
 		"Subject: %s\r\n"+
+		"Message-ID: %s\r\n"+
+		"MIME-Version: 1.0\r\n"+
 		"Content-Type: %s\r\n"+
+		"Content-Transfer-Encoding: 8bit\r\n"+
+		"Date: %s\r\n"+
 		"\r\n"+
 		"%s\r\n",
 		strings.Join(m.To.RawStrings(), ", "),
 		m.From.String(),
 		m.Subject,
+		m.MessageID,
 		m.Type,
+		m.Date.Format(time.RFC1123Z),
 		m.Body,
 	)
 }