Hi,

If the user setup the account as IMAP on all three devices, it doesn't seem to be related to the ISP side since there is no such issue on the other two devices - it is only with the Outlook 2013 client.

I would suggest the user make sure all folders have been subscribed, which is usually the cause of such issues. As you already did, I suspect the Outlook data file may have been corrupted. Outlook stores the account information in the data file and if it's corrupted, you may meet issues like emails not received.

Let's try with the tool Scanpst.exe to scan and repair the possible errors in the user's data file(.ost):

https://support.microsoft.com/en-us/kb/272227

Regards,

Melon Chen
TechNet Community Su