Exchange 2016 CU18 (Any Limitation for Shared Mailbox connect Outlook?

Sathishkumar Singh 61 Reputation points

Hello Support

We are handling more clients. so we have created 35 Shared Mailbox

When we give delegate 35 Shared Mailbox to Users.

Our User facing issues like Outlook Disconnected frequently.

Some delegates added may not show up automatically in Outlook. Outlook is limited to displaying only the first 32 entries (If a delegate user has an archive, the user counts as 2 entries).

Is there any limitation of adding Mailboxes in Outlook?

How can i design as per our requirement?

What is the best practice? Cached Mode or Online
Currently i am using Cached Mode in Outlook

is it good practice to Use Online?
What are the impacts if i use Online?

Kindly advise

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Andy David - MVP 115K Reputation points MVP

    Best practice is to have the primary in cache mode and the shared mailbox not cached:


    Limitations for on-prem get a bit tougher:

    32 sessions sounds about right:


    MAPI on the Middle Tier (MoMT) n/a 32

    However, it can tough to manage that because there are also throttling considerations:

    Bottom Line Recommendations:

    1. Run Outlook in cache mode
    2. Do not download Shared Mailboxes. Uncheck that option.
    3. Limit the number of shared mailboxes uses can open. Consider not auto-mapping them to a user if they require access to more than 10 or so.,the%20AutoMapping%3A%24false%20parameter.

    Add-MailboxPermission -Identity <Mailbox ID1> -User <Mailbox ID2> -AccessRights FullAccess -AutoMapping:$false  
    1 person found this answer helpful.

  2. Yuki Sun-MSFT 26,856 Reputation points

    Hi @SathishkumarSingh-4967

    As per your concern about the Cached mode and Online mode, basically Cached Exchange Mode is the preferred (and default) configuration in Outlook client. It no longer depends on continuous network connectivity and most users find it works faster than Online mode.
    However, considering the fact that the larger the data file, the more application pauses or performance issues you may experience, agree with Andy that it's recommended to keep running the primary account in Cached mode, and meanwhile, disabling the caching of all shared folders by Clearing the checkbox of "Download shared folders".

    Here's an official document about Cached Exchange Mode and Online Mode for your reference:
    Plan and configure Cached Exchange Mode in Outlook 2016 for Windows

    Regarding the limit of 32 sessions, please refer to the suggestions provided by Andy to disable the auto-mapping. Furthermore, you may consider creating some public folders instead for shared access to information within your organizations. See Public folders.

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