Outlook 2024 slows down massively when using remote credential guard

Question

I would like to share some information here that might save one or the other admin who is in charge of Office and/or network security a few gray hairs. Also, I hope some MS office developers read this and ask themselves how this is possible and fix it!

Namely: after switching from Office 2016 to Office 2024 LTSC (on premises Office, on premises Exchange Server), I noticed that the start of Outlook took a very long time (up to 15 seconds) and switching from one email to the next could take up to a sporty 10 seconds, depending on the size of the attachments.

After a thorough analysis, it became clear that this extreme only occurs if you use Outlook in a remote session AND also have the security feature Remote Credential Guard ("RCG") activated. I had connected to the office computer via RDP from the home office with a PC with active RCG via VPN, and that made the Outlook started on the office computer almost unusable in the new version.

So it is clearly the case that Outlook 2024 LTSC constantly (when any mail is previewed or opened!) passes the user credentials to the server (for whatever reason), while previous versions probably did not. If you are now connected via WAN and have passed your credentials through RCG, this is a massive problem, as every credential request costs time due to high WAN latencies. After I deactivated RCG, everything was immediately as fast as before.

For anyone who has this problem, it is recommended to disable RCG on the endpoints that are connected via WAN.

Versions, for the sake of completeness:

Client OS: Win11 23 H2, Build 10.0.22631.4602

Outlook version: 2408 (17932.20190)

Exchange Server: 2019 CU 14

PS: don't confuse RCG with normal credential guard ("CG"). This is really only about RCG.

Answer 1

Hello, @MTG,

Welcome to the Microsoft Q&A platform!

Thank you for sharing this detailed information! It sounds like you encountered a very specific issue related to Outlook 2024 LTSC and Remote Credential Guard (RCG).

Here is my summary for your information:

After upgrading from Office 2016 to Office 2024 LTSC, Users noticed significant delays in Outlook performance during remote sessions using RDP and active Remote Credential Guard (RCG). Specifically, opening Outlook took up to 15 seconds, and switching between emails with attachments could take up to 10 seconds. A thorough analysis revealed that this issue arose because Outlook 2024 LTSC frequently sends user credentials to the server, a behavior that is impacted by WAN latencies when RCG is active. Disabling RCG on endpoints connected via WAN resolved the performance issues. This recommendation is specifically for RCG and not normal Credential Guard (CG).

Your analysis and solution will likely be very helpful to others facing the same problem.

Disabling RCG on endpoints connected via WAN can indeed help resolve the performance issues with Outlook when using RDP sessions. It's always good to double-check network latency and authorization mechanisms for any impact on performance, especially when updating or changing software versions.

If you have any other tips or need assistance with anything else, feel free to let me know!

---

In order to make answer searching in the forum easier and be beneficial to other community members as well, please consider accepting the answer to help increase visibility of this question for other members of the Microsoft Q&A community. Thank you again for helping to improve Microsoft Q&A!

Best Wishes,

Alex Zhang