Question / Problem:
KTA is no longer deleting emails from the Outlook inbox on ingestion and instead is ingesting the same email over and over again. Rebuilding the Outlook inbox resolves the issue temporarily until some limit is hit again and the issue resurfaces.
Answer / Solution:
The limit was a 7 yr retention policy on the MS exchange. Once the deleted files hit capacity it would no longer allow for inbox purge. Once all of the deleted items where archived functionality returned. See:Retention tags and retention policies in Exchange Server