Hi @alfonsojon, thanks for reaching out!
Bitwarden does not support OAuth for email, only SMTP. As far as we know, SMTP AUTH is still available to send messages through Microsoft, but you should research before enabling and configuring for your Bitwarden self-hosted server. From Microsoft: Setup for SMTP AUTH, and setup for the device. This option is usually not turned on by default. As always, the setup for Bitwarden server settings is in our FAQs here.