The problem seems to be fixed. Sorry for the little disgression ;)
Quoting Bashar <big at kuwaitnet dot net>:
> W'Salam Mehdi,
>
> Basically Exim mailserver (and others too) has a feature where you can
> set to verify the sender's email address on the sending mailserver if
> it does not exists it will deny the message to help decreasing spam.
>
>
> feel free to email me privately off the list so we don't go out of the
> subject of the thread :)
>
>
> Best Regards,
>