SMTP test
Connects to your mail server and checks the greeting, EHLO, STARTTLS, the TLS certificate and reverse DNS, with the time each step took.
Ready for mail
gmail-smtp-in.l.google.com:25TLSv1.3gmail-smtp-in.l.google.com answers on port 25 (server-to-server delivery) with TLSv1.3 with a trusted certificate. The greeting, EHLO, STARTTLS and reverse DNS all check out. The session took 179 ms.
4 passed, 1 for informationNothing to do here. Open it to see the detail.The greeting name differs from reverse DNSReverse DNS confirmedGreeting in 33 msSTARTTLS works, TLSv1.3EHLO lists 6 extensionsShowHide
Session
Each step of the conversation, in order, with how long the server took.Certificate
TLSv1.3, TLS_AES_256_GCM_SHA384.EHLO extensions
What the server says it supports.MX records for gmail.com
The test used the first one. Test the others too: senders fall back to them.Transcript, 22 linesC is our test, S is the server. Our test host's name and IP are hidden.ShowHide
SMTP settings for common providers
For mail clients, apps and sequencers. Mailbox providers take the full email address as the username; the email APIs give you SMTP credentials in their dashboards.Next
What the SMTP test does
Enter a domain, a mail server's name or its IPv4 address, and pick a port. For a domain, the test connects to its highest-priority MX; a name with no MX is tested as the server itself. It records the 220 greeting and the EHLO reply, upgrades the connection with STARTTLS, checks the certificate, then looks up the IP's reverse DNS and confirms that name resolves back to the same address.
The session ends with QUIT right after EHLO and STARTTLS. The test never sends MAIL, RCPT or DATA, so no message is sent.
How to read the session
- Greeting: the 220 reply and the name the server gives itself.
- EHLO: the extensions the server supports. STARTTLS should be listed, and AUTH should appear only after TLS starts.
- STARTTLS and TLS: whether the upgrade works and which TLS version it negotiates.
- Certificate: whether the chain is trusted, whether it covers the server's name, and how long it has left.
- Reverse DNS and FCrDNS: the IP's PTR name, and whether that name resolves back to the same IP.
Each step shows how long the server took. A greeting that takes several seconds is often a deliberate pause against spam bots.
Ports 25, 587 and 465
Port 25 carries mail from server to server, and TLS on it is opportunistic. Port 587 is the submission port from RFC 6409, used by mail clients and apps with STARTTLS and a login. Port 465 is submission over implicit TLS, which RFC 8314 now recommends for clients. Each run tests one port.
Most cloud providers block outbound port 25 by default, so a test from a laptop or a cloud server can fail even when the mail server is fine. This test runs from a server with port 25 open, so a timeout here means the mail server or its firewall didn't answer.
Why it matters for cold email
If you run your own sending servers, Gmail requires valid forward and reverse DNS for every sending IP and TLS on the connection. A missing PTR record, or one that doesn't resolve back, gets mail rejected or junked at many receivers.
If you send through Google Workspace or Microsoft 365, their servers handle this. Test your own MX instead, to confirm replies can reach you, and any SMTP relay your sequencer sends through.