[otrs] Question on otrs replying to users

Hi, First time here, just finished installing otrs. I'm having some issues... When a user sends an email to otrs@domain.com, the OTRS box replies but replies with otrs@localhost.localdomain. How can I change this as if the user replies to the response from OTRS, it fails as the exchange system does not know about otrs@locahost.localdomain... It need to have a specific @domain.com My second issue is: I use fetchmail on the otrs user to get the emails from the exchange, and drop them to the local mail folder of otrs. Although the emails are not put in to OTRS specific queue... How is this done? Regards, Thanks in advance for your help. Nelson