What is the limit of Outlook clients connected to the same Exchange Account.

[Wesley De Bruyne]

Hi,

Does anybody know what the limit is of Outlook clients connected to the same Exchange Account?

We have 2 Exchange Tenants (A & B). We have 20+ users from tenant A that want to add one and the same mailbox of tenant B to their outlook. However we now can't add this anymore. We get this error when we try to add this maibox to new users:

The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.

Forwarding the mails is not an option since we need to reply with the same e-mailadres to mails that enter mailbox B.

Grtz

[#2]

Here is a link to a page that details this:  https://technet.microsoft.com/en-us/library/ff477612(v=exchg.141).aspx

You want to pay close attention the "Session Limits". As this is what applies to you.  Based on the default parameter - you're looking at 16 user sessions per server - which is likely what's tripping you up.

[#3]

Hi, well i've seen this and it might be unchanged in the past 6 years and might be the same in Exchange Online. What i've found in the meantime is that the limit in exchange online could be 20 and that you can ask msft to increase this limit. So now i have created a ticked with this question. I'll post my findings back here.

[#4]

Ok just got it confirmed by Microsoft the max amount concurrent sessions are 40.

When mapping the mailbox using user credentials 4 connections are opened: 2 for Azure AD, 2 for Exchange. so that devides the limit to 10. It can nog be increased (only during migration) so i'm stuck and out of luck :)

[#5]

Do the same limits apply when connecting using Outlook on the Web?

[#6]

Hi, 

I was informed by Microsoft upon enquiring about the server-side thresholds, that the EWSMaxConcurrency is set to 27. This value also appears in this article https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/ews-throttling-in-e..., and is set in each tenant's throttling policy. 

Best regards,

Markus

[#7]

As others have kind of pointed out here too, keep in mind every client/connection will add more, and reduce the number of connections you can have.

So if you have a user who sets up an account on his PC at work, Ipad, and phone, than they are likely taking up more than you realize. As the above response says, a good rule of thumb we found was roughly 4 connections per user, but if the user has multiple devices you cannot count on that being true.

We ultimately decided shared mailboxes etc were the way to go, and stopped trying to share user logins between systems.

Adam