SEC-03 / SECURITY
SMTP Port Tester
Test common mail, web, and hosting control panel ports on a public host.
About the SMTP Port Tester
Email and web services rely on specific TCP ports being reachable — SMTP on 25, submission on 587, IMAPS on 993, and so on. If a required port is closed or firewalled, the corresponding service won't work. This tool probes common mail, web, and control-panel ports on a public host.
What this tool checks
It attempts TCP connections to a set of common ports (SMTP, submission, POP3, IMAP, HTTP, HTTPS, and hosting control panels) on the host you enter, and reports which are open. Private and internal addresses are blocked for safety.
Reading the results
An open port means the service is reachable from the internet. A closed port could mean the service isn't running, or that a firewall is blocking it. For mail servers, ports 25, 587, and 465 are the ones that matter most.
Frequently asked questions
Which ports does an email server use?
SMTP uses port 25 for server-to-server delivery, 587 for authenticated submission with STARTTLS, and 465 for implicit TLS submission. POP3 uses 110/995 and IMAP uses 143/993.
Why is port 25 blocked?
Many ISPs and cloud providers block outbound port 25 by default to curb spam. This is why authenticated submission on port 587 is preferred for sending mail from applications and clients.
What does a closed port mean?
A closed port means no service accepted the connection — either nothing is listening on that port, or a firewall is blocking it. For a service you expect to be running, check the service status and firewall rules.