Dutch users problems

We have a mixed environment using the ms lotus connector for mail from exchange into domino for Notes webmail users.the problme is everytime Netherlands users email the webmail people they are crashing my HUB.

Only these users and it is always a dutch language emails.

The messages stay in the mail.box instead of going to the exchange .box and routing properly.

Could these be return receipts that are not working properly?

Could it be the original sender has an invalid or incorrect return address setup for themselves?

Happenned on 7.00, 701, 701fp1 and now 702.

Ideas, exorcisms, help?