rejected email from external mail server "Authenticated sender:"

[dabanfi at libero.it]

Sorry form my question, may be stupid but I've  a problem with kolab 2 
(probably configuration problem)

I've set differents client email as pippo at mydomain.local and defined as 
internet email as pippo at mydomain.it

The system working fine (receive and send email) but some email server 
reject my email with this message:

i.e I send a email to ciccio at demo.org, after I received a Mail message from 
the 
destination server as:

<ciccio at demo.org>: host mail.demo.org[xx.yy.zz.xx] said: 550
    Domain demo.org does not accept mail from
    ip-116-76.static.adsl.mydomain.it (in reply to MAIL FROM command)

I suppose the problem is located in the 'Authenticated sender:' item, 
becuase the domain is different for
the 'From' field (Authenticated sender:pippo at mydomain.local , From: "pippo" 
pippo at mydomain.it)

I'm shure that may be my setting error, but I try to look were make the 
correct setup but I don't found nothing

Any help is aprecied

Daniele Banfi