Receiving emails with blank FROM and SUBJECT field from Novel systems

We have Exchange 2003.  Occasionally we receive emails that arrive with blank FROM, TO, and SUBJECT fields. I have discovered the one thing in common with these emails is that they are all from Novel mail servers (Groupwise.) I have spoken with the Sys Admins that manage these systems and they don't know why this would be happening. In fact, we are currently doing business with someone at Novel itself, and their emails arrive like this on a regular basis. I'd figure if anyone would be aware of an issue like that it would be them, but no one over there has been able to figure it out, aparently.

Other mail systems (such as Lotus) arrive without any problem.  It only occurs with Groupwise.

I have researched the issue and can't find any documentation on other people experiencing this issue.  Has anyone seen this problem before? Any thoughts on probable causes?

Thanks!