Hi we have an issue where several users mailboxes will occasionally re-download the entire OST. There may be days or weeks before the occurrence, but when it happens, the mailbox downloads several GB of data again. This is an issue because they have to restart Outlook repeatedly to see new emails, not to mention the bandwidth consumption.

I've done New-MailboxRepairRequest to check for corruption on the mailboxes, but the mailboxes have no issues. I've tried re-creating the mailbox profile as well but the issue comes back after days or weeks. I don't see anything particularly relevant in the Event Logs.

What should I look for to resolve this?

Hi ,

1.Does all the affected mailboxes residing in the same mailbox database ?

2.Just move anyone of the problematic mailbox to a different database and check the results ?

2.Does all the affected mailboxes has a huge size on the exchange mailbox ?

3.For anyone of the problematic account please delete the existing ost file and check the status ?

4.Please check is there is any latest update installed on those client machines is creating these kind of problems ?

5.For anyone of the problematic user Please disable the antivirus and check the results ?

6.For anyone of the problematic user what happens when you try to run the outlook on the safe mode ?

7.For anyone of the problematic user account please disable the add-ins and check the results ?

8.For anyone of the problematic user account please move the existing items to the pst file and check the same issue is occurring  for the new items arriving in the exchange mailbox ?

Hi,

Any updates? Have you checked Nithyanandham's suggestion.

Please make sure the problematic users can work with their mailboxes well in OWA. In client side, please make sure there is no third-party program which is related to mail scanning installed. If there is, please disable them to have a try.

Additionally, please disable using Exchange Cached mode and use Outlook in Online mode to check whether the message can be send and received\updated correctly. If the issue can be reproduced in Online mode, please change a new clean computer for the problematic user and check whether the issue persists.

Regards,