Help & Troubleshooting
SMTP Server
What this is
This check connects to your domain's highest-priority MX host on port 25, reads the greeting, sends EHLO, and inspects the advertised capabilities — the same first steps every sending server performs when delivering you mail.
How to read your result
Healthy: a 220 greeting naming your mail host, and STARTTLS among the EHLO capabilities. Important caveat: many networks (including cloud hosts) block outbound port 25, so a timeout from this tool can be the tool's environment rather than your server.
Common problems and how to fix them
Mail server does not answer on port 25
How it shows up: Inbound mail from the whole internet bounces with connection errors — or, if only this tool times out but mail flows fine, the tool's network is simply blocked.
How to fix it: Verify with an independent test from another network. If genuinely down: check the mail service is running, port 25 is open in every firewall/security-group layer, and the MX points at the right host.
STARTTLS not offered
How it shows up: All inbound mail arrives over plaintext connections; MTA-STS cannot be deployed; some senders downgrade or complain.
How to fix it: Enable STARTTLS in the mail server with a valid certificate for the MX hostname (self-signed works for opportunistic TLS but fails MTA-STS). On managed mail hosting this should already exist — if missing, escalate to the provider.
Greeting hostname mismatches the MX name
How it shows up: Elevated spam scores and occasional rejections from strict receivers.
How to fix it: Configure the server's announced hostname to match the MX record and give that name matching forward and reverse DNS.