I have one user, possibly two, who are having problems sending email internally to all users. Both are caching. When they send to everyone, approximately 70 out of 380 recipient show Undeliverable with a date three minutes after the email was sent, or Pending with a date of 12/31/1969 5:00 PM.

Most, if not all, the undeliverable and pending items are in the same PO as the sender.
The addressed are all internal and appear to be correct.
The emails are not sent with any delayed delivery.
Performing a Send/Receive does not change the status of any of the undeliverable or pending items.
Running a local GWcheck on caching mailbox did not fix the issue.

Any help in troubleshooting this issue would be greatly appreciated. For time being, I have user most affected user switched over to Online mode

GW version is 8.0.1 on NetWare. I know we need to upgrade to 8.0.2 hp3, but not an option to upgrade at this time. Unless upgrade is known to fix this issue.