Connecting to an Exchange server requires an implementation of the MAPI interface.
Mail is capable of communicating with IMAP servers but MAPI is not implemented.
There are plans to use EDS as a backend for Mail in the future. EDS can connnect to Exchange.
I am running Loki stable and have found a work around for now. By adding the account as an "Other" online account in Online Accounts, the account shows in Mail and I can send/receive messages.
Connecting to an Exchange server requires an implementation of the MAPI interface.
Mail is capable of communicating with IMAP servers but MAPI is not implemented.
There are plans to use EDS as a backend for Mail in the future. EDS can connnect to Exchange.
Setting this bug report to wishlist.