This happens because you are using somewhere in your system the address OTRS@localhost.localdomain
And localhost.localdomain  is not a DNS resolved MX domain, of course.
Change it with a real email address.
Da: otrs-bounces@otrs.org [mailto:otrs-bounces@otrs.org] Per conto di Stefano Milziadi
Inviato: mercoledì 12 novembre 2008 14.23
A: User questions and discussions about OTRS.
Oggetto: [otrs] Mail Delivery Subsytem Error

Hi!
 
I am receiving every 5 minute some messages in the RAW Queue (now there are 35 messages) where the content is:
"root@localhost
(reason: 553 5.5.4 <OTRS@localhost.localdomain>...Real domain name required for sendere address)
(expanded from: root@localhost)"
 
How can I resolve this problem?

Regards,

--
Stefano Milziadi
pepozzo@gmail.com