==== Required information ====
- iRedMail version: 0.8.7 (Pro 1.8.2)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Linux/BSD distribution name and version: Debian Wheezy
- Related log if you're reporting an issue:
====

One of our users have a @qsl.net alias that forwards mail to firstname.lastname@mydomain_a.com.

We have tested when sending from a e-mail address on an other domain towards the alias (and the alias should then forward that mail to firstname.lastname@mydomain_a.com).

We do see what the error message say, but why do the sender get this? Is it any secure way to solve this on our side? Or should it be fixed on the other end?

Error message:

------- Forwarded message -------
From: "Mail Delivery System" <MAILER-DAEMON@mailman.qth.net>
To: firstname.lastname@mydomain_a.com
Cc:
Subject: Undelivered Mail Returned to Sender
Date:

This is the mail system at host mailman.qth.net.

I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own text from the attached returned message.

                     The mail system

<firstname.lastname@mydomain_a.com> (expanded from <user_alias@qsl.net>): host
      hostname.myserver.com[MY.IP.AD.DDR] said: 553 5.7.1
<firstname.lastname@mydomain_a.com>:
      Sender address rejected: not logged in (in reply to RCPT TO command)