Loss Of Groupwise Email

A Novell 4.11 server with Groupwise 5.2 is losing about 20 % of incoming EMail.

There are 20 user licenses for Novell & 15 User licenses for Groupwise.

Most EMail is delivered OK, but there seems to be a consistant 20 % missing.

Any ideas and is the difference in license numbers, just a coincidence.

Many thanks

Sean