Does Mailspring support Microsoft Exchange Web Services or ActiveSync?
Unfortunately, Mailspring does not support Exchange (Exchange Web Services or ActiveSync), nor do we plan to support this in the future. Presently, you may be able to connect to your Exchange server via IMAP. Note that not all Exchange versions support this feature.
We also plan to improve OAuth support for Exchange servers authenticating that way. Watch this topic for the latest on that effort: Institutional Office365 not working
For a full list of the providers Mailspring supports, see: Supported Email Providers