Check What Authentication Are Accepted on a Smtp Server (With Msmtp)
Fleeting- External reference: https://github.com/marlam/msmtp/issues/57
msmtp -S –host=outlook.office365.com –port=587 –tls=on –tls-starttls=on
AUTH: Supported authentication methods: LOGIN XOAUTH2
The error message says that ‘basic’ authentication is disabled, which means the LOGIN method (although in that case they should not say that it is supported in response to the EHLO SMTP command, but that’s another topic). Which means you must use auth xoauth2 in your configuration file, with the password set to your OAuth2 token. How to get such a token depends on the service and I cannot help with that; msmtp merely passes it on to the server.