Forgejo has mailer functionality for sending transactional emails (such as registration confirmation). It can be configured to either use Sendmail (or compatible MTAs like Postfix and msmtp) or directly use SMTP server.
Please note: authentication is only supported when the SMTP server communication is encrypted with TLS or `HOST=localhost`. TLS encryption can be through:
- STARTTLS (also known as Opportunistic TLS) via port 587. Initial connection is done over cleartext, but then be upgraded over TLS if the server supports it.
- SMTPS connection (SMTP over TLS) via the default port 465. Connection to the server use TLS from the beginning.
- Forced SMTPS connection with `IS_TLS_ENABLED=true`. (These are both known as Implicit TLS.)
Note: For Internet-facing sites consult documentation of your MTA for instructions to send emails over TLS. Also set up SPF, DMARC, and DKIM DNS records to make emails sent be accepted as legitimate by various email providers.