Issue: The timestamp for sent emails is changing between the hours of 5:00 - 9:00 PM EST. All day, emails are sent/replied and show the correct timestamp in the sent folder until sometime between the hours of 5:00 - 9:00 PM.

Potential Corrective Actions:
Attempted resync to the server. No Change.
Verified filesystem. No Issues.
Verified date/time. Correct.
Verified regional settings. Correct.

Between the hours of 3:30 PM and 6:07 PM, the computer was in the process of running a chkdsk /r /x. (No issues found.) No changes to the client side OST file during this time. When Outlook was logged in, the SENT folder was checked and the timestamps were correct until it had a chance to resync to the server, where the timestamps then changed on all the previous days sent items from valid sent time to a non-valid sent time 5:28 PM.

Does anyone have any ideas what could be causing this issue and why there would be a process that is changing the timestamp?

Thanks in advance.