matrix-docker-ansible-deploy/docs/configuring-playbook-email.md

Adjusting email-sending settings (optional)

By default, this playbook sets up a postfix email server through which all Matrix services send emails.

The email server would attempt to deliver emails directly to their final destination. This may or may not work, depending on your domain configuration (SPF settings, etc.)

By default, emails are sent from matrix@<your-domain-name> (as specified by the matrix_mailer_sender_address playbook variable).

Furthmore, if you'd like to relay email through another SMTP server, feel free to redefine a few more playbook variables. Example:

matrix_mailer_sender_address: "another.sender@example.com"
matrix_mailer_relay_use: true
matrix_mailer_relay_host_name: "mail.example.com"
matrix_mailer_relay_host_port: 587
matrix_mailer_relay_auth: true
matrix_mailer_relay_auth_username: "another.sender@example.com"
matrix_mailer_relay_auth_password: "some-password"