ERROR: [5002-21-218-80020009] Unable to migrate attachment, while migrating email from source to target.
This will happen when an attachment cannot be accessed by the Migrator for some reason (e.g., it's corrupted, it's a shared file owned by another account, or the attachment has been stripped by a virus scanner if one is present on the migration server.
The Quest migration tools use the Novell Admin API's to extract mail data so one way to confirm if a message is corrupt is to log into the Groupwise mail account and see if you can open the attachment.
If the messages corrupted were from the Archive Mailbox, try to move the message to PostOffice Online & move back to Archive Mailbox again
RUN GWCHECK 2 & 3 times to ensure there is no other corrupted message being detected after moving the corrupted message.
By moving the corrupted message online & offline or vice versa, will actually or sometime resolved the message corrupted issue that unable to migrate using Groupwise Migrator.