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.

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What Is the SMTP Connectivity Checker?

It finds a domain's mail server and tries to open connections on the standard SMTP ports: 25 (server-to-server delivery), 465 (SMTP over TLS) and 587 (submission).

When to Use It

When a mail server is not receiving mail.
After changing firewall rules on a self-hosted mail server.

How to Use It

Enter the domain.
See which ports accepted a connection.

Understanding the Result

Port 25 must be open on a server that receives mail from the internet. Hosted services such as Gmail accept mail on 25 at their MX hosts, while 465 and 587 are used by mail clients sending mail.

Limitations

It only tests whether a connection opens, with a short timeout; it does not send email or test authentication. Many cloud providers block outgoing port 25 from their own servers.

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mail server itself may be down, a firewall is blocking all SMTP traffic, or the MX record is pointing to an incorrect/outdated host - this warrants immediate investigation since it likely means incoming mail delivery is currently failing.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.