[Feature]: Grommunio first class support

[deajan]

Is your feature request related to a problem?

As of today, mail-archiver can interact with Grommunio via IMAP.
The problem is that Grommunio's IMAP implementation copies an exchange database into IMAP format, and as such takes almost twice the disk space, and is not very performance efficiant.

Describe the solution you'd like

Adding support for EWS protocol would allow using mail-archiver with Grommunio as well as on-premises Exchange servers.

Additional context

I do understand that implementing EWS protocol isn't just a ews=true line.
But it would also solve the "I need a username and password for each IMAP account" problem, since we can have delegates in EWS.

Just my two cents, knowing if this feature would be worth considering.