The following message can be found in mail target agent and calendar/public folder logs:
"CReceiver::AddFile TraceMsg 3406 Item '/o=COMPANY_NAME/ou=First Administrative Group/cn=Recipients/cn=USER_NAME' was added to the collection 'COLLECTION_NAME'. The PST file ('00173184C2B9E7409D033680C0C4158E.PST') has been processed 546 time(s) before."
By Design with legacy agents.
This is by design. Mail target agent or public folder/calendar agents archive an incoming PST file that cannot be processed. This can be specified on the agent's Properties page. By default, after 32 unsuccessful attempts to process .PST file, it gets archived.
This does not apply to the situations when the agent has failed to login into the mailbox. Under typical circumstances, like corrupted data in .PST file, it is generally getting archived after 32 attempts, by default.