History We are migrating Exchange 2010 to 2019. We are at the middle point with Exchange 2016 and 2010 is still running.


Server Environment Active Directory Domain Level: 2012R2 Domain controller count: 4 x3 DCs running 2012R2 x1 DCs running 2022 x1 Exchange 2010 server x1 Exchange 2016 server

Client Environment #1 Windows 10 Pro Desktop Outlook v16 (x86) (Microsoft 365)

Client Environment #2 Windows 2022 Datacenter Outlook v16 (x86) (Microsoft 365)

Client Environment #3 Windows 2012R2 Datacenter Outlook v16 (x86) (Microsoft 365)

Client Environment #4 OWA hosted on the Exchange 2016 server accessed via Chrome Problem Description

In all Client environments where the Outlook client is used, a user is unable (usually) to re-open the Outlook client after closing it. After the Outlook client goes into its failed state, the following message is returned when the program is launched.

"Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed."

This failed state will persist for approximately 15 minutes before the client returns to a working state. Alternatively, to get the client back to a working state the "Exchange Back End" website, hosted on the Exchange 2016 server may be restarted. Doing so immediately allows clients to connect to the Exchange server.

I've spent hours upon hours troubleshooting this and am getting no where. Does anyone have any advice?



  • Have you checked the network connection or firewall between client and server? Are there any other event logs?
    – Ivan Lv
    Oct 24, 2023 at 8:10
  • Hi, please check the connection diagnostic tool of Outlook, and let us know what error you see, as is your problem is hard to diagnose without that log. (learn.microsoft.com/en-us/outlook/troubleshoot/connectivity/…)
    – yagmoth555
    Oct 24, 2023 at 14:11
  • @IvanLv, there doesn't seem to be any interruption network wise. In fact its only the 2nd attempt to run the client that runs into an issue. The first attempt connects just fine. Oct 24, 2023 at 15:56
  • @yagmoth555, I've been paying close attention to the connection monitor while troubleshooting. After standing up the 2016 server we did have quite a few connection issues but those have been ironed out now. When the client opens the first time things connect as expected. After re-opening the client two connections are made and it will consistently fail the third. That persists for about 15 minutes or until the Exchange Back End website is restarted. Oct 24, 2023 at 15:58

1 Answer 1


Time for an update,

With the help of a third party, we seem to have a working solution. We edited and applied the default throttling profile to affected users. The specific setting that was changed was RcaMaxConcurrency. The default was set to 40 so we opened that up to unlimited and applied it to only affected users. Once that took affect the affected users have not yet had the issue reappear. It's also worth mentioning that this edit was made after we migrated to 2019. The problem presented the same across 2016 and 2019 but we only figured out a solution after the migration to 2019.

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