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Use the TCP port checker to test whether a host and port accept a connection from the test service. It opens a connection and sends a line break. It does not verify SMTP, TLS or any other application protocol.
Open the TCP port checker. Extended API calls use your Spotzee credit balance; see pricing for current rates.

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Check a connection

1

Choose the destination

Use the hostname or public IP address and port supplied by the service owner. For API access, send domain_ip and port as form fields to POST /generic/dns/tcp-verifier.
2

Read the result

The response contains data.connection: success when the connection and write complete, or fail when they do not. A failed connection can still return HTTP 200, so inspect the result field.
3

Investigate a failure

Check the host, port, DNS and firewall configuration. The result does not distinguish a refused connection, a timeout or a failed write. Test from your own sending environment too, because its network access can differ.
For SMTP submission, use the port and encryption mode required by your provider. A successful TCP result does not confirm credentials or message acceptance. Use the SMTP email test for that next check.