And how about the way Microsoft IMAP support is broken
I spent a happy few days proving that Microsoft Exchange is truly broken when it comes to IMAP support.
It seems that, if a message contains a meeting request, then downloading via IMAP will silently modify the message to strip the meeting request and replace it with a link to the OWA meeting instead! After all, can't have those pesky 3rd-party mail-and-calendaring tools working now can we?
In addition, if they find a MIME-wrapped message then they can automatically re-wrap it in lovely tnef format for you, coincidentally breaking your mail client.
Both of these behaviours can be disabled; but only per mailbox, not as a default, and only via some tortuous (undocumented) powershell.
During this process, I phoned up the MS Support people (stupid move, I know, but we pay for them and I have to show I tried). The minion I spoke with insisted Microsoft Exchange did not do this, even when I presented him with the powershell code to fix it, and the steps to duplicate it.
Exchange 365 is an absolute nightmare to administer when you've come from something as simple as Dovecot under Unix.