To add a Microsoft 365 / Exchange account to eM Client as IMAP or POP3 with OAuth authentication, use the manual account setup:

1. Go to Menu > Accounts (Windows) or eM Client > Accounts (macOS)
2. Click '+Add account'.
3. In the New Account window, select Mail > Other.
4. Insert your MS365 account address.
5. For the incoming IMAP or POP3 server, enter: outlook.office365.com
6. For the outgoing server, enter: smtp-mail.outlook.com
7. Continue the setup. You will be redirected to your browser to grant access via OAuth.