Testeur SMTP

Check that a mail server answers, negotiates TLS, and accepts your login - step by step

100 % gratuit. Cet outil a besoin de notre serveur pour effectuer le travail : ce que vous soumettez y est traité puis supprimé, il n'est jamais conservé.

Test a login (optional)

Used for a single AUTH check on this one connection and never stored or logged. Prefer an app password over your main one.

shield This tool cannot send email. It stops at authentication, on purpose - a "send a test message" button would make the endpoint usable as a spam relay.

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À propos de cet outil

Find out why mail is not going out. This tester speaks SMTP to the server exactly as a mail client would: it opens the connection, reads the greeting banner, sends EHLO, upgrades the session with STARTTLS where it is offered, inspects the TLS certificate, and - if you supply credentials - checks that authentication is accepted. Every step is timed and shown with the actual server reply, so instead of a vague failure you get the precise point where things break. It deliberately cannot send email, which keeps the endpoint from being usable as a spam relay.

Flux de travail

Résoudre un e-mail qui n'est pas livré

Confirmez que le serveur répond et que vos identifiants fonctionnent avant d'accuser le DNS.

  1. 1Tester le serveur SMTPConnectivité, TLS, certificat et AUTH.Vous êtes ici
  2. 2Vérifier le DNS inverséUn enregistrement PTR manquant est une cause fréquente.Ouvrir
  3. 3Inspecter les enregistrements DNSVérifiez que SPF et MX sont publiés.Ouvrir

Comment utiliser cet outil

  1. Enter the server and portUse 587 for modern submission with STARTTLS, 465 for implicit TLS, or 25 for server-to-server relay.
  2. Optionally add a loginSupplying a username and password adds an AUTH check. They are used for that one connection and never stored.
  3. Read the traceEach step shows whether it succeeded, how long it took and what the server actually replied - which is usually where the problem is obvious.

Pourquoi l’utiliser

  • A step-by-step trace with real server replies, rather than a single pass or fail.
  • TLS certificate subject, issuer and expiry, with a warning when it is close to expiring.
  • Lists the AUTH mechanisms and capabilities the server advertises after the TLS upgrade.
  • Re-reads capabilities after STARTTLS, which is where AUTH usually appears - checking before the upgrade reports it as missing.
  • Cannot send email by design, so it is safe to run against your own production server.
  • Credentials are used for one session and never logged or stored.

Usages courants

  • Working out why an application cannot send email through a provider.
  • Confirming that a new mail server is reachable and negotiating TLS before going live.
  • Checking whether an app password has been accepted after rotating credentials.
  • Verifying that a certificate renewal actually took effect on the mail service.
  • Deciding whether to use port 587 with STARTTLS or 465 with implicit TLS.
  • Confirming a firewall rule opened the submission port from the outside.

Conseils pour de meilleurs résultats

  • Use an app password rather than your main account password wherever the provider offers one.
  • Port 465 is always implicit TLS; the encryption selector follows the port automatically.
  • If STARTTLS is not advertised, the server may only accept encryption on a different port.
  • A 535 reply to AUTH means the credentials were rejected, not that the server is broken.
  • Certificate expiry inside 30 days is flagged - renew before it bites.
  • If the banner never arrives, the port is usually blocked rather than the server being down.

Erreurs à éviter

  • Expecting a test email to arrive - this tool stops at authentication and never sends mail.
  • Testing port 465 with STARTTLS selected; 465 expects TLS from the first byte.
  • Reading no AUTH mechanisms as a fault when the server only advertises them after STARTTLS.
  • Using a main account password where the provider requires an app-specific one.
  • Assuming a successful login means delivery will work - SPF, DKIM and DMARC are separate matters.

Questions fréquentes

No, deliberately. A public endpoint that sends mail to any address you name is an open relay, so this tool stops at authentication. That still answers the questions people actually have: is the port reachable, is TLS working, has the certificate expired and are the credentials right.

They are used for a single AUTH command on that one connection and are never written to storage or logs. We still recommend an app password rather than your primary one, which is good practice for any third-party tool.

The four standard SMTP ports: 587 for submission, 465 for implicit TLS, 25 for relay and 2525 as a common alternate. Restricting the list is what stops the tool being used as a general port scanner.

Most servers only advertise AUTH after the connection is encrypted. We re-send EHLO after STARTTLS for exactly that reason, so an empty list usually means the server genuinely offers no authentication on that port, or STARTTLS did not complete.

Once a TLS certificate expires, clients that verify it will refuse to connect and mail stops flowing. The expiry date is shown on every test and flagged when it is within 30 days so you can renew before that happens.

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