No, i did it and it has the required domain name at the sender part thanks a lot!!!!!! : )
But when i send it from the web interface, domainname.tld/squirrelmail it still has the primary domain appended.
Do you think it might be related to the mail server i'm using? I don't know if I must set up a new mail server for that or if i can just use the older one (mail.1st_domain.tld) as the mail server.