Once upon a time there was a server. Lets call it zzz.com, running Ubuntu LTS 10. Then, domain owner decided to create his corporate mail via Google Apps, and created account firstname.lastname@example.org.
Everything looks to be fine with email@example.com. Mail is sent / received.
But there is one mysterious problem. When PHP script at zzz.com is trying to send some mail to [ANYNAME]@zzz.com, mail is not delivered. Sendmail works fine when trying to send mail anywhere else.
There is a non-delivery notification in this case in the mail log.
What could this be? How can this be fixed?