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smtp: add Date and Message-ID headers to outgoing mail

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RFC 5322 requires both headers. Date uses RFC1123Z formatting; Message-ID
is a random 16-byte token scoped to the sending domain parsed from From.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Astra 2026-09-11 17:39:55 +01:00
parent f1c24e483c
commit 3289882dbd
1 changed files with 23 additions and 0 deletions
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23
internal/otpdelivery/smtp/sender.go
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@ -3,7 +3,9 @@ package smtp
import ( import (
"bytes" "bytes"
"context" "context"
"crypto/rand"
"crypto/tls" "crypto/tls"
"encoding/hex"
"fmt" "fmt"
"mime" "mime"
"net" "net"
@ -146,6 +148,8 @@ func buildMessage(from, to, subject, body string) []byte {
var b bytes.Buffer var b bytes.Buffer
b.WriteString("From: " + from + "\r\n") b.WriteString("From: " + from + "\r\n")
b.WriteString("To: " + to + "\r\n") b.WriteString("To: " + to + "\r\n")
b.WriteString("Date: " + time.Now().Format(time.RFC1123Z) + "\r\n")
b.WriteString("Message-ID: " + generateMessageID(from) + "\r\n")
b.WriteString("Subject: " + mime.QEncoding.Encode("utf-8", subject) + "\r\n") b.WriteString("Subject: " + mime.QEncoding.Encode("utf-8", subject) + "\r\n")
b.WriteString("MIME-Version: 1.0\r\n") b.WriteString("MIME-Version: 1.0\r\n")
b.WriteString("Content-Type: text/plain; charset=utf-8\r\n") b.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
@ -155,6 +159,25 @@ func buildMessage(from, to, subject, body string) []byte {
return b.Bytes() return b.Bytes()
} }
// generateMessageID builds a Message-ID header value (RFC 5322 3.6.4), using
// the sending domain parsed out of the From address and a random token so
// each message gets a unique id even under concurrent sends.
func generateMessageID(from string) string {
domain := "localhost"
if addr, err := stdmail.ParseAddress(from); err == nil {
if i := strings.LastIndex(addr.Address, "@"); i >= 0 {
domain = addr.Address[i+1:]
}
}
var raw [16]byte
if _, err := rand.Read(raw[:]); err != nil {
// crypto/rand failing is effectively unheard of, but fall back to a
// time-based token rather than emit a non-unique Message-ID.
return fmt.Sprintf("<%d@%s>", time.Now().UnixNano(), domain)
}
return fmt.Sprintf("<%s@%s>", hex.EncodeToString(raw[:]), domain)
}
// emailContent builds the login-code email subject/body, branded with the // emailContent builds the login-code email subject/body, branded with the
// operator's configured product name (Config.AppName) instead of the // operator's configured product name (Config.AppName) instead of the
// package's internal "telesrv" fallback. // package's internal "telesrv" fallback.