Open
The host accepted a connection on the port.
Free TCP port check
Check that a host accepts TCP connections on a port, and how long the connection takes.
- Free, with no signup
- Saves nothing it checks
What your result means
Port 25
This check cannot test port 25. Test a mail server's submission ports, 587 and 465, instead.
Closed
The connection was refused, or got no answer within 6 seconds.
Questions about the TCP lookup
Which ports do mail servers use?
Port 25 between mail servers, 587 for sending with STARTTLS, 465 for sending over TLS, and 993 and 995 for reading mail.
Why can port 25 not be tested?
The network this check runs on blocks outgoing connections to port 25, as many cloud networks do to stop spam.
Does the check send anything?
No. It opens one connection, notes the time, and closes it.
Found a problem? We will check the rest.
Book a deliverability audit and we will look at every domain and mailbox you send from.