updates

sitesvc/internal/mail/mail.go

@@ -1,7 +1,9 @@
 package mail
 
 import (
+	"crypto/rand"
 	"crypto/tls"
+	"encoding/hex"
 	"fmt"
 	"mime"
 	"net"
@@ -135,6 +137,12 @@ func message(from, to, subject, body, replyTo string) []byte {
 	if replyTo != "" {
 		b.WriteString("Reply-To: " + sanitizeHeader(replyTo) + "\r\n")
 	}
+	// Date and Message-ID are RFC 5322 essentials. Without them many servers
+	// accept the message at SMTP time and then silently junk or drop it, and
+	// SpamAssassin scores MISSING_DATE and MISSING_MID heavily — the message
+	// "sends" but never lands in the inbox.
+	b.WriteString("Date: " + time.Now().Format(time.RFC1123Z) + "\r\n")
+	b.WriteString("Message-ID: " + messageID(from) + "\r\n")
 	b.WriteString("Subject: " + mime.QEncoding.Encode("utf-8", sanitizeHeader(subject)) + "\r\n")
 	b.WriteString("MIME-Version: 1.0\r\n")
 	b.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
@@ -143,6 +151,21 @@ func message(from, to, subject, body, replyTo string) []byte {
 	return []byte(b.String())
 }
 
+// messageID builds a unique <id@domain>, taking the domain from the From
+// address so the identifier matches the sending domain. Falls back to the host
+// name when From has no domain part.
+func messageID(from string) string {
+	domain := "vantage.local"
+	if at := strings.LastIndex(from, "@"); at >= 0 && at < len(from)-1 {
+		domain = strings.Trim(from[at+1:], "<> ")
+	}
+	var buf [16]byte
+	if _, err := rand.Read(buf[:]); err != nil {
+		return fmt.Sprintf("<%d@%s>", time.Now().UnixNano(), domain)
+	}
+	return fmt.Sprintf("<%s@%s>", hex.EncodeToString(buf[:]), domain)
+}
+
 func sanitizeHeader(v string) string {
 	return strings.NewReplacer("\r", " ", "\n", " ").Replace(v)
 }