Your Mail Server Can Be “Up” and Still Be Broken
A TCP connection succeeding on port 25 or 587 tells you almost nothing. The real question is whether your mail server correctly negotiates EHLO, advertises the extensions clients expect, and completes a STARTTLS handshake without a certificate mismatch any one of which can silently fail after a config change, a certificate rotation, or a software upgrade.
Seabhac.io connects like a real mail client would and verifies the full handshake, not just that something answered the socket.
How it works:
- Connect on schedule: Open a real SMTP connection to your mail server on the port you specify.
- Negotiate EHLO: Send the EHLO greeting and capture the full response, including every advertised extension.
- Verify STARTTLS: Confirm the TLS handshake completes cleanly, catching certificate mismatches before a mail client does.
What Actually Goes Wrong
- STARTTLS downgrade or failure after a certificate renewal points the wrong chain at the mail port.
- Missing extensions (like
PIPELININGor8BITMIME) after a server migration, silently degrading performance or breaking certain clients. - Unexpected banner or greeting changes that indicate someone modified the server configuration without telling you.
Caught the Moment It Happens
Because checks run continuously from distributed probes, a handshake regression is caught within minutes of deployment — not the next time someone tries to actually send mail through that server and it bounces.