Outlook Connected to Exchange, but only downloads mail sporadically

David Harron 1 Reputation point
2020-09-08T22:14:43.923+00:00

We have a three users with Outlook 2016 and 365 who are connected to Exchange, but do not get their mail regularly. The status bar message is stuck on "Updating Inbox" until after an hour so they suddenly receive the half dozen emails that they are missing. Their email then works normally for a few hours until the cycle repeats. There are many users whose email continues to work normally, the people affected have more email than average, but there are many people with lots of email who are unaffected.
Web mail works normally and shows the delayed email for the affected users.

The connection status troubleshooting screen that I access with a Ctrl+Right click on the tray icon shows Outlook connected to our exchange server the whole time. All of the users are in cached mode because they have too much email that they all want to keep handy and non-cached mode is too slow.
I have tried completely reinstalling Outlook, recreating their outlook profile, adding an exception to the OST file in our Antivirus tool, deleting and rebuilding the .ost and telling outlook to check for mail every 5 minutes even when offline, none of this has made a difference.

Does anyone have any suggestions as to what this could be or how to fix it?

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Jade Liang-MSFT 9,976 Reputation points Microsoft Employee
    2020-09-09T08:04:57.803+00:00

    Hi @David Harron ,

    The status bar message is stuck on "Updating Inbox" until after an hour so they suddenly receive the half dozen emails that they are missing.

    Is this issue only recent? If so, did you do any specific operations before it?
    Have you tried to shorten the offline time(like 3 days) in Cache Exchange mode to check if the issue has any difference?

    Due to you have tried many operations(such as completely reinstall Outlook and recreate their outlook profile etc.), this issue seems not be related to your Outlook Client. To further analyze it, please try to log these problematic email accounts into other Outlook clients which could work normally and see if the issue has any difference.

    If they could work fine on those normal Outlook clients, the issue may be related to your local windows settings, please ensure that you are working with latest Ethernet drivers and Windows.Besides, for more assistance, it's suggested to download SaRA tools which could figure out what's wrong and offers some solution for the identified problem.

    If issues can also be reproduced in other normal Outlook clients, based on the similar thread I found, the MTU settings in server might cause issues like this. It's suggested to check your settings and see if it works.(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)

    Hope above information is helpful to you.

    If the response is helpful, please click "Accept Answer" and upvote it.
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