Port 587 (SMTP submission)
Authenticated mail submission from clients, upgraded to TLS with STARTTLS.
- Transport
- TCP
- Internet exposure
- Public by design
Normally public, but keep the software patched and hardened.
Security notes
- A target for credential stuffing against mail accounts.
- Require TLS before authentication.
When it shows up in your logs
Authentication failures across many accounts is password spraying.