Email Tools

SMTP Connectivity Checker

Test whether a domain's mail server can be reached on the standard SMTP ports.

Checks TCP reachability only - no authentication or SMTP commands are sent.

Not sure what to enter? Try an example: gmail.com

Free & instant No signup How to use FAQ

Enter a domain to find its mail server and test connections on ports 25, 465 and 587.

What does an SMTP connectivity check do?

It finds the domain's mail servers from its MX records and tests whether they accept connections on the standard SMTP ports - 25 for server-to-server delivery, 465 and 587 for submission. If port 25 is unreachable, other servers cannot deliver mail to the domain.

How to test SMTP connectivity

Enter the domain in the box above.
Click Check SMTP.
Review which mail servers and ports responded.
If a port is closed, check your mail server's firewall and your hosting provider - many block port 25 by default.

Related checks

To list the mail servers first, use the Mail Server Lookup.
To check MX priorities, use the MX Record Checker.

JustChecker monitors your mail server's reachability continuously.

Frequently Asked Questions

Port 25 must accept connections for other servers to deliver mail to you. Ports 587 and 465 are used by your own email apps to send mail through the server.

If your MX server can't be reached on port 25, other servers can't deliver to it and will retry, then bounce. Check the server, its firewall and your hosting provider.

No. It only checks that the server answers on each port; nothing is sent.

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