Is there a limit to the number of mailboxes (shared and delegated) that you can view in Outlook at one time

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Is there a limit to the number of mailboxes (shared and delegated) that you can view in Outlook at one time

Robb4242 46

We have an owner/CEO who runs (micromanages) the main company and 4 separate sub-entities. This person has a mailbox for each entity. They also have access to multiple shared mailboxes (accounting, HR, etc) for each entity. In addition, they are delegated to some mailboxes for some of the C-suite members current & past. The issue this person is facing now is that some mailboxes initially open in Outlook, but then disappear within 3 - 5 seconds of opening.

The question I have is, does Outlook have a limit on the number of mailboxes it can open and operate at one time? If there isn't a limit, does anyone have an idea of why these mailboxes (usually the shared) appear & then disappear after Outlook opens.

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Vasil Michev 119.7K MVP Volunteer Moderator

All software has limitations. Depending on the version of Outlook, it can be 10-20, and is increasable via reg key. But that's only part of the issue, as caching/profile bloat quickly starts becoming a problem as the number of mailboxes grows.

Best get him to use OWA/the webmail instead. He can open separate tabs for each additional mailbox, add direct links to them as bookmarks or have them added to collections, etc.

Alternatively, setup forwarding so he can receive all (or at least some) of these messages addressed to these mailboxes directly in his own.

Robb4242 46 Reputation points

2025-02-07T17:29:16.0433333+00:00

I appreciate the reply and both alternatives are good, and we've mentioned both to her. We've already dealt with some of the caching/profile bloat issues as well and I suspect that may be why the mailboxes are disappearing.

She doesn't want webmail because "Outlook is better" (her position) and forwarding emails would just get lost and she can't keep everything separated (and she doesn't have time to deal with creating rules). I was really hoping for something documented that we could show her in writing because once we have documentation, she'll usually back down on her expectations.
Vasil Michev 119.7K Reputation points MVP Volunteer Moderator

2025-02-07T17:44:48.1133333+00:00

Well if you believe that will convince her, here's the KB on "slow shared mailbox performance": https://learn.microsoft.com/en-us/outlook/troubleshoot/performance/slow-performance-if-having-many-shared-folder-or-mailboxes-open
Robb4242 46 Reputation points

2025-02-07T18:26:57.9166667+00:00

Thank you!!! My google-fu has been off this year. If that doesn't satisfy her, not much else we can do.

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Is there a limit to the number of mailboxes (shared and delegated) that you can view in Outlook at one time

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