Groupwise 5.5.4 message delivery problem

We cannot send or receive messages with attachments that are larger 5 meg. I’ve checked all the settings for GWIA access control, SMTP relay, and just about every other setting I can find–nothing works. The message that is returned with the undeliverable mail is:
DATA 552 Message exceeds maximum fixed size (5242880)

Sometimes the messages bounce within 5-10 minutes, sometimes it takes overnight. The property status of the message shows as transferred.

Any ideas out there?

TIA,
mertmrountre@electricities.org