Could perhaps someone help me with this ?

I have a "domain.com" working perfectly, with mails directed/handled by Google Apps.
I also have a "domain.eu" pointing to "domain.com". Both web sites are OK.

However, when someone send a mail to …@domain.eu, it is always rejected: "The error that the other server returned was: 550 550 authentication required (state 13)" or "Delivery to the following recipients failed".

Any idea on how to solve this ?

THANK YOU VERY MUCH in advance for any help!
Have a nice weekend,

Paul
pzveny@gmail.com