SMTP Test
Connect to any SMTP mail server from our EU servers and see its greeting banner, the extensions it advertises (STARTTLS, AUTH and more), and whether the session completes.
About SMTP Test
SMTP Test opens a live TCP connection to the mail server and hostname and port you specify, then walks through the opening of an SMTP conversation exactly as a sending mail server would. It reads the server's greeting banner, sends an EHLO command, and parses the multi-line reply that lists the server's capabilities. You get back the raw banner, a clear connected/not-connected status, and a badge for each key feature - including whether STARTTLS (encryption upgrade) and AUTH (authenticated submission) are offered - plus the full list of advertised extensions.
The default port is 25, the standard port for server-to-server mail transfer, but you can test any port: 587 for authenticated submission, 465 for implicit-TLS submission, or a custom port your provider uses. This makes the tool useful for confirming that a firewall or cloud provider is not silently blocking outbound port 25, that a newly configured MX host answers at all, and that the server advertises the extensions your clients depend on.
The check is read-only and diagnostic: it reads the banner and capabilities and then issues QUIT - no message is sent, no mailbox is probed, and no credentials are used. The whole session has a nine-second timeout, so an unreachable or filtered host returns a clear timeout error rather than hanging. Because the connection originates from our own EU-based servers, the result reflects what an external internet host sees when it tries to reach your mail server, which is often different from what you observe from inside your own network.
A healthy result is a 220 banner followed by a 250 EHLO response that lists extensions. A missing banner, a truncated capability list, or a connection that never completes usually points at a firewall rule, a greylisting or reputation filter, or a misconfigured listener - all things worth catching before they turn into stuck mail.
How to use it
- 1Enter the mail server hostname you want to test, such as the MX record for a domain (for example mail.example.eu).
- 2Set the port - 25 for standard mail transfer, or 587 / 465 / a custom port for submission - leaving it at 25 if unsure.
- 3Click Test SMTP to open the connection from our EU servers.
- 4Read the banner and the connected status, then check the STARTTLS and AUTH badges and the list of advertised extensions.
- 5If the test times out, verify the host answers on that port from the public internet and that no firewall is blocking it.
Common use cases
- -Confirming a newly set up mail server or MX host responds correctly before pointing live mail at it.
- -Checking whether outbound port 25 is reachable to a given host, or being blocked by a firewall or cloud provider.
- -Verifying that a mail server advertises STARTTLS so client and server-to-server connections can be encrypted.
- -Diagnosing delivery problems by comparing what an external host sees against what you see from inside your own network.
- -Auditing a provider's SMTP endpoint to see which extensions and authentication methods it supports.
Frequently asked questions
- What does an SMTP test actually check?
- It opens a TCP connection to the mail server, reads its greeting banner, sends EHLO, and lists the extensions the server advertises - including STARTTLS and AUTH. It confirms the server is reachable and responding correctly without sending any email.
- What is port 25 used for?
- Port 25 is the standard port for SMTP server-to-server mail transfer between mail servers. Ports 587 and 465 are used for authenticated client submission. This tool defaults to port 25 but can test any of them.
- Does the SMTP test send an email or need my password?
- No. The test is read-only: it reads the banner and EHLO capabilities, then sends QUIT. No message is delivered, no mailbox is probed, and no credentials are ever entered or required.
- Why does my SMTP test time out?
- A timeout usually means the host is unreachable on that port from the public internet - commonly because a firewall or cloud provider blocks outbound port 25, the wrong hostname or port was entered, or no mail service is listening there.
- How do I know if a mail server supports STARTTLS?
- Run the test and look for the STARTTLS badge and the STARTTLS entry in the advertised extensions list. If it appears in the EHLO response, the server can upgrade the plaintext connection to an encrypted TLS session.
- Why test from an external server instead of my own machine?
- Because the result reflects what other mail servers on the internet actually see. Our EU servers connect from outside your network, revealing firewall rules, port blocks, or reputation filters that you would not notice testing from inside.