SMTP Test

Check whether a mail server accepts connections and responds correctly — connectivity only.

This tool never asks for, uses, or stores a mailbox password — it only opens a connection, reads the server's banner, and sends EHLO before disconnecting.

What is an SMTP test?

An SMTP test checks whether a mail server accepts connections and responds the way a mail server should. SMTP, the Simple Mail Transfer Protocol, is how email moves between servers and from email apps to servers. This SMTP test connects to the server you choose, reads its greeting banner, introduces itself with an EHLO command and lists the features the server offers, then disconnects politely.

It is a connectivity check only. It never asks for a password, never logs in and never sends a message.

How the SMTP test works

You enter a mail server hostname or IP address and choose a port. The tool resolves the name, refuses private or internal addresses, and opens a connection with a six-second limit. It reads the banner, sends EHLO, records the server's response and then sends QUIT. Each connection can run 10 tests per minute.

Which port to test

  • 25 (SMTP): used between mail servers to deliver incoming mail.
  • 587 (Submission): used by email apps to send mail, upgraded to encryption with STARTTLS.
  • 465 (SMTPS): also used for sending, with encryption from the very start of the connection.

How to run an SMTP test

  1. Enter the mail server, for example mail.example.com. Use the MX Lookup if you do not know it.
  2. Choose port 25, 587 or 465.
  3. Press Test Connection.
  4. Read the banner and the EHLO response.

Reading the SMTP test results

Banner

The first line a server sends, starting with code 220. It usually includes the server's hostname and sometimes its software.

EHLO response

Lines starting with 250 list the server's capabilities. Common ones include STARTTLS, meaning encryption is available; SIZE, the largest message accepted; AUTH, the login methods offered on submission ports; and PIPELINING and 8BITMIME, which are efficiency features.

No connection

The server did not answer on that port within the time limit, or the connection was refused. The error message explains which.

Why connections fail

Many home internet providers and cloud networks block outgoing connections on port 25 to stop spam, and some mail servers only accept connections from known networks. A failed test on one port is therefore not always a fault. Try the other ports, and compare with the result your email provider expects.

Understanding SMTP reply codes

Every server reply starts with a three-digit code. Codes beginning with 2 mean success, such as 220 for a server that is ready and 250 for an accepted command. Codes beginning with 4 are temporary failures, so a sender should try again later. Codes beginning with 5 are permanent failures, such as a refused command. The first digit tells you most of what you need to know.

Common uses

  • Checking that a mail server is online after maintenance.
  • Confirming STARTTLS is offered before setting up an app or device.
  • Finding which sending port works for a printer, website or scanner.
  • Checking the hostname a server announces in its banner after a migration.

Common problems and fixes

Could not connect. The server refused or did not accept the connection on that port. Confirm the hostname and port with your email provider.

Connection timed out. A firewall may be blocking the port, or the server is down. Check your server's firewall rules and that the mail service is running.

No STARTTLS in the EHLO response. Encryption is not enabled on that port. Install a certificate on the mail server and enable TLS.

The destination cannot be tested. The server resolves to a private or internal address, which cannot be reached from the internet.

Related tools

Frequently asked questions

Does the SMTP test send an email?

No. It connects to the mail server, reads its greeting, sends an EHLO command to see the server's capabilities and then disconnects with QUIT. It never logs in, never sends a message and never asks for a password, so it is safe to run against any public mail server.

Which SMTP port should I use?

Mail servers deliver to each other on port 25. Email apps, websites and devices should send through port 587 with STARTTLS, or port 465 with encryption from the start. Your email provider's settings page tells you which of the two submission ports it supports.

Why does the SMTP test fail on port 25?

Port 25 is often blocked by internet providers and cloud networks to stop spam, and some servers only accept connections from known networks. The server might also be down or behind a firewall. If ports 587 or 465 connect, the server is probably running normally.

What does STARTTLS mean in the results?

STARTTLS in the EHLO response means the server can switch the connection to encrypted TLS before any message is sent. Without it, mail on that port may travel unencrypted. Most modern mail servers offer it, and many receiving servers prefer or require it.

What is an SMTP banner?

The banner is the first message a mail server sends after a connection opens, starting with code 220. It normally contains the server's hostname and sometimes its software. A banner hostname that matches the server's reverse DNS name is a good sign of a well-configured server.

Can I test my email login with this tool?

No. The tool is limited to connectivity and never handles usernames or passwords. To test a login, use your email app's account settings, which connect directly with your credentials. If the connection test here works but login fails, the problem is with the credentials or authentication settings.

How many SMTP tests can I run?

Each connection can run 10 SMTP tests per minute, which is plenty for troubleshooting. The limit keeps the tool from being used to hammer mail servers. If you see a message asking you to wait, try again after a minute.