SMTP tester
Point it at any mail server. We connect from our network and report the ports that answer, the greeting, the TLS certificate, the capabilities, whether your login works, and — if you want — send one real test email and show the queue id. Every reply the server gives is in the transcript.
What each check means
- Port scan — which of 25/465/587/2525 answer, with the greeting. A timeout is a firewall or block, not a mail problem.
- Encryption — STARTTLS or implicit TLS, protocol and cipher, and whether the certificate matches the hostname, is trusted, and is not expiring.
- Capabilities — the EHLO response: AUTH mechanisms, SIZE limit, PIPELINING, 8BITMIME, SMTPUTF8, DSN.
- Login — AUTH PLAIN/LOGIN with your credentials, only over TLS, and the server's exact reply (235 accepted, 535 rejected, 534 app password required).
- Test email — a real message through the server to an address you choose, so you can confirm delivery and inbox placement.
- Open relay & blocklists — for server admins: does the box relay for strangers, and is its IP on Spamhaus, SpamCop or Barracuda.
Provider settings
Not sure of the host or port? Use the preset above or read the settings page: Gmail, Office 365, Outlook.com, Zoho, Amazon SES, SendGrid, Hostinger, cPanel — or all 38 providers.
Test our relay
Host smtp.queensmtp.com, port 587 or 465. Credentials come with a free account: 100 emails a day, then $5/year plus $0.10 per 1,000.
SMTP tester — questions
It resolves the host, connects from our network, reads the 220 greeting, sends EHLO and lists the capabilities (SIZE, AUTH mechanisms, PIPELINING, 8BITMIME, SMTPUTF8, DSN), negotiates STARTTLS or implicit TLS and reports the certificate (name match, issuer, expiry), attempts AUTH PLAIN/LOGIN if you give credentials, can send one real test email to an address you choose, probes for open relay, and checks the server IP against Spamhaus, SpamCop and Barracuda. Every step is timed and the full transcript is shown.
The password is used for one AUTH command over TLS and discarded; it is never stored or logged, and the transcript masks it. The tester refuses to send a password on a connection without TLS. If you prefer, run the port scan and connection test without credentials first.
The tester runs from our servers. If it succeeds and your app times out, your app's network blocks the port (clouds block 25; Linode blocks 25/465/587 on new accounts) — run the port scan, then use whichever port answers, or a relay.
A fixed plain-text message with the server, port, encryption and login result. Nothing you type is put in the message — only the recipient and From address you give. It is limited to three test emails per hour per visitor.
A server that accepts mail for foreign domains without authentication. The tester sends MAIL FROM and RCPT TO for an external address without logging in and reports whether the server accepted it; no message is sent. An open relay gets blocklisted within hours.