Microsoft has released security updates for vulnerabilities found in:
Exchange Server 2013
Exchange Server 2016
Exchange Server 2019
All versions (Cumulative Update levels) are impacted. ...
Updated Aug 05, 2021
Version 15.0
Blog Post
Hi Nino,
I have a case open with support, I can email you the case number privately if you'd like. We've experienced extreme Outlook slowness/poor connectivity since installing Exchange 2016 CU21. Disabling AMSI has resolved the symptoms, but I'd love to see the problem resolved rather than disable an important feature.
I use Sophos, but I've seen mentions on forums of users with other AV products having the same issue.
First mention I found, sorry it's in German but easy to translate: https://www.frankysweb.de/exchange-2016-2019-amsi-integration-sorgt-fuer-probleme-mit-outlook/
Note that remarking out the AMSI lines in the web.config did not solve the problem for me, only disabling AMSI in the Sophos product.
There are a couple of mentions in this reddit thread: https://www.reddit.com/r/exchangeserver/comments/oaf63p/june_updates_for_exchange_2016_and_2019_released/