A group of emails disappeared from a user's deleted items folder.
He had 2200 emails in his deleted file, and now it shows 1600. From 1/5/16 - 1/22/16 are gone. Older and newer emails remain.
I was able to get them back from the "recover deleted items" but that doesn't explain why only some emails have disappeared from his deleted items. He said this has happened in the past. We are on Outlook 2010 Exchange and we do not use Email Retention.