Is there a documented maximum number of users you can have connected to an Office 365 user mailbox?

Question

We have a user mailbox on Office 365 that we share out to a department at our company with around 20 users. We've had some problems with the mailbox regularly updating for some users.

Utilizing a Shared Mailbox is not an option due to the size and required functionality of the mailbox (sending out emails via TLS through O365).

We're being told by our Vendor of Record that provides support (as a middleman) for Office 365 that you cannot have that many users connected to a user mailbox with Office 365 but I cannot locate any documentation to support such a claim.

Thanks in advance for any assistance.

Are the users connecting to the mailbox with the credentials for that mailbox, or are they using their own credentials and "Full Access"" rights? — longneck, Mar 02 '15 at 16:30
They are using their own credentials and full access rights. — Windows Ninja, Mar 03 '15 at 11:01

score 2 · Accepted Answer · answered Mar 18 '15 at 16:47

I received the following feedback from Microsoft with regards to throttling in place for Office 365:

The throttling limit for attribute “RCAMaxConcurrency”, which defines the number of concurrent connections allowed from Outlook, is set to 40 which translates to roughly to roughly 14 max conncections from Outlook 2007/2010/2013 clients to the mailbox.

However, Microsoft also recommended a workaround for this would be to use a Shared mailbox which would get around this problem as Shared mailboxes are not handled the same as User mailboxes on Office 365.

Hope this helps somebody else in the future!

score 1 · Answer 2 · answered Mar 02 '15 at 16:11

1

It's not a hard limit of endpoints or users, it's about throttling policy settings. Each endpoint, whether Outlook (MAPI), or mobile (EWS typically), will use a number of connections. That number may be 1, or it may be higher. Each connection will do certain things like connect to AD, or search, or send mail, etc. When you hit a throttling limit for a type of behavior over a type of connection, future connections will be throttled.

(User vs Shared mailboxes will make no difference to O365. It's still a mailbox.)

answered Mar 02 '15 at 16:11

mfinni

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Is this a setting that can be controlled within Office 365? – Windows Ninja Mar 02 '15 at 17:04
You should ask your vendor for help. This isn't something that's exposed to administrators, you'll have to work with MS for this. And it would be a good idea to formulate what actual problem you're having, because you haven't actually stated a technical problem in your question. – mfinni Mar 02 '15 at 17:06
You're right, I should have included that in my question. The mailbox stops updating for several users for extended periods of time. – Windows Ninja Mar 03 '15 at 09:01

Is there a documented maximum number of users you can have connected to an Office 365 user mailbox?

2 Answers2