I have a a user who has a subfolder that the retention policy doesn't seem to work on.  If the emails were imported form say a pst could that be reason?  what are the best options for troubleshooting this?  I have turned on logging but nothing shows up.  Thanks.  

retention policy will work only when the mailbox size is above 10MB. Till that time it will just mark the items for deletion and when the mailbox size reached 10MB, it will remove the items based on the policy we defined.

Also the user is having more than 1000 subfolder in his/her outlook ?

Hi  KirkSH,

Thank you for your question.

What is mean by your state which is If the emails were imported form say a pst could that be reason?

Could you tell us more details which is about your retention policy?

If the retention policy didnt work for the specific user, we could check if the specific user has been included in retention policy, then make sure AD replication without any problems, then we could rebuild the outlook profile to check if the issue was solved, we could also check it in OWA.

If the retention policy didnt work for all user, we could check if the retention policy tags has been included in the retention policy.

We could refer to the following link:

https://social.technet.microsoft.com/Forums/office/en-US/1761ae96-8f4c-44b2-83a4-3ddb8f80201d/delete-emails-from-inbox-in-exchange-2010-and-not-subfolders?forum=exchangesvradminlegacy

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim