Hi George,
From what I know, Outlook itself has few limitation regarding the number of mails, folders or the mails in folders, etc. But there might be some limits enforced by mail hosts. Based on my research, with Outlook syncing to a mail host via IMAP, the limits
will be a lot lower than Exchange Server. The exact values depend on the mail host and IMAP software used so check with the hosts for details. For your concern about the limits in mail hosts side, you may contact the mail service provider for more information.
In Outlook client side, are these affected machines running the same version of Outlook?
Does this issue affect all IMAP accounts in your environment?
Besides, there have been reports that the sync problem could be resolved by removing the setting that states to show only subscribed folders in Outlook. Please try the steps below and see if it can be helpful:
- Right-click the name of your account with the issue, then click the IMAP Folders... link.

-
Uncheck the checkbox of "When displaying hierarchy in Outlook, show only the subscribed folders."
-
Force sending/receiving within Outlook and see the result.
Regards,
Yuki Sun
Please remember to
mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact
tnsf@microsoft.com.
Click
here to learn more. Visit the dedicated
forum to share, explore and
talk to experts about Microsoft Teams.