Update: NTLM is now supported in eM Client 8.2 and newer

In case you're trying to set up an Exchange account in eM Client for Mac and you're getting pop-ups with failed authentication, then your mail server most likely requires an NTLM authentication, which is currently not supported in eM Client for Mac.

We are aware of the problem and are collaborating with Microsoft on a solution that will solve this once and for all.

A possible workaround is setting the account up with IMAP protocol manually via eM Client > Add account > Mail > Other or ask your mail server administrator if there are some other authentication methods available for Exchange protocol on your server.