- Please note: authentication is only supported when the SMTP server communication is encrypted with TLS or `HOST=localhost`. TLS encryption can be through:
- Via the server supporting TLS through STARTTLS - usually provided on port 587. (Also known as Opportunistic TLS.)
- SMTPS connection (SMTP over transport layer security) via the default port 465.
- Forced SMTPS connection with `IS_TLS_ENABLED=true`. (These are both known as Implicit TLS.)
- This is due to protections imposed by the Go internal libraries against STRIPTLS attacks.