For a cuple of days there has been a problem for users sending e-mail to certain domains (buisness related domains, not MSN, AOL etc). Email get queued on the Exchange server. Contacted the admin on the other side but he was not very helpful. It also seems that the problem is random.
The user on my domain receives: Your message has been successfully relayed to the following recipients but the requested delivery status notifications may not be generated by the destination.
The relay Restriction is set to "Only the list below" +Adresses=LAN + the box with Allow all computers is checked.