Email Tools
SMTP Connectivity Checker
Check whether a domain's mail server is reachable on standard SMTP ports (25, 465, 587).
Enter a domain to check whether its mail server is reachable on standard SMTP ports (25, 465, 587). No authentication is attempted.
Checks TCP reachability only - no authentication or SMTP commands are sent.
JustChecker monitors your mail server's reachability continuously.
Frequently Asked Questions
Port 25 is the traditional server-to-server mail relay port (often blocked by ISPs/cloud providers to fight spam); port 587 is the standard for authenticated mail client submission; port 465 is the older, implicit-TLS submission port - which ports should be open depends on your mail server's actual role.
Many cloud/hosting providers block outbound port 25 by default specifically to prevent spam from compromised servers - if your mail flows through an authenticated relay or managed email service instead, port 25 being closed is often expected, not a misconfiguration.
It suggests the mail server itself may be down, a firewall is blocking all SMTP traffic, or the MX record is pointing to an incorrect/outdated host - this warrants immediate investigation since it likely means incoming mail delivery is currently failing.
No - it tests basic TCP-level connectivity (whether the port is open and accepting connections), not full authentication or message delivery, which would require actual mail server credentials.
A port being open only confirms network-level reachability - actual delivery also depends on authentication credentials, sender reputation, SPF/DKIM/DMARC alignment, and the receiving server's own spam filtering, none of which this specific connectivity check evaluates.
No - this is a standard, read-only TCP connectivity test, equivalent to what any mail client or server routinely does when attempting to establish a legitimate connection.