[Macha]

Some email providers support oauth. For some of those (Microsoft and Google), Thunderbird does support the oauth flow. However, how you connect oauth to email is not really standardised, so my understanding is even though "it's all oauth", these implementations are a lot more vendor specific than you'd expect.

Also the need for the email client to have a relationship with the oauth provider is probably a discouragement for some of the smaller email providers to move to oauth.