Forum Discussion
Copied sent items of shared mailbox not recognized by 3rd party mail systems
We have in Office 365 / exchange online, multiple shared mailboxes where the option MessageCopyForSentAsEnabled is true. This way as somebody sent an email with the shared mailbox as sender, it doesn...
It's definitely "known", but I haven't been successful as to obtaining a proper answer if it's a bug or a feature. I have a more detailed article on it here, including and explanation of why it works like this (sort of): https://www.michev.info/Blog/Post/1947/messagecopy-settings-and-forwarding
But if you want an official answer, best open a support case.