Our configuration: GW 8.0.2hp1 on Netware 6.5.8

One of our partners uses Lotus Notes, and regularly sends us appointment
requests for meetings and conference calls.

We receive most appointment requests without issue, but we have had
several users recently miss important conference calls and other
appointments due to not receiving the appointment requests. The GWIA
logs do show the requests coming into the system.

One user told me that he briefly saw an incoming appointment request hit
his mailbox late last week (apparently for a conference call he missed
yesterday). But it quickly disappeared from his mailbox (only visible
for a fraction of a second) without ever being
selected/opened/accepted/declined/etc. It didn't go to the trash or
junk mail, and a search of his account didn't find it anywhere else
either. If he hadn't been looking at the GroupWise client at the exact
time it happened, he wouldn't have seen it at all. He was able to
glimpse the subject matter, which happened to be the topic of the
conference call, and we later found out coincided with when the
appointment request was sent to him.

We have no rules in place at all for the affected users, but it is
almost as if the incoming appointments are automatically deleted or
declined, but the senders believe we have accepted the appointments.

Besides using Lotus Notes, the only other thing I've noticed is that the
sending system apparently uses Simple Private Signatures / Bounce
Address Tag Validation (the sender address is always in the form
prvs=value=user@example.com). I don't know that this matters, but I
thought I'd mention it.

I'm stumped. Any ideas?