Apple has announced via their MobileMe System Status page:
MobileMe members may experience delays sending and receiving messages using their MobileMe Mail address.
Service will be restored ASAP. We apologize for any inconvenience.
All other MobileMe services are online and fully operational.
Last updated: 4/30/2009, 11:54 PT
Source: Apple’s MobileMe System Status
[Thanks to MacDailyNews Reader “DavidO” for the heads up.]