Microsoft has released Security Updates (SUs) for vulnerabilities found in:
Exchange Server Subscription Edition (SE)
Exchange Server 2019
Exchange Server 2016
SUs are available for the f...
Updated Jul 14, 2026
Version 6.0
Blog Post
We installed the June update and are experiencing issues with Shared Mailboxes where 'MessageCopyForSentAsEnabled' is enabled.
We are still in Hybrid mode with Centralized Transport enabled with almost all of our users in Exchange Online.
After installing the June update users are still able to send mails from the shared Mailboxes, and a copy of the sent mail appear in the sent items folder in the shared mailbox.
The issue arrise when the mail is sent to an external recipient and routed through the on-premises servers. The on-premises hybrid servers uses the builtin transport agent 'SharedMailboxSentItemsRoutingAgent' and send a forwarded message back to the Shared Mailbox with the original mail attached.
Is this something you have seen and have a solution for?
Yep, seeing same issue. This is confusing to our end-users and adding extra work.