---
title: TCP and SMTP monitoring
description: Knowing a port is open is not the same as knowing why connecting to it is slow. TCP port monitors now show a connection-timing waterfall so you can see where…
canonical: https://watchfor.io/changelog/2026-05-10-tcp-smtp-monitoring
---

[All updates](/changelog/page/9#2026-05-10-tcp-smtp-monitoring) ✨ New May 10, 2026 · v 1.2.8

# TCP and SMTP monitoring

Knowing a port is open is not the same as knowing why connecting to it is slow. TCP port monitors now show a connection-timing waterfall so you can see where the time goes, and SMTP monitors include a built-in open-relay check, so a misconfigured mail server is caught before spammers find it.

Where the time of each connect goes.

STARTTLS and the open-relay test in one check.

## TCP

A TCP monitor connects to a host and port, such as db.example.com:5432 . The waterfall splits every connect into the DNS lookup, the TCP connect and, with Use TLS , the TLS handshake, so a slow resolver looks different from a slow server.

- TCP Connect Time is on as a warning above 1000 ms.

- Response Match sends a string after connecting and checks the reply against a regular expression: a Redis PING , a mail banner, a line-based health check.

## SMTP

An SMTP monitor connects to your mail server, says EHLO, checks that STARTTLS is offered and tests whether the server will relay mail for anyone.

- Open Relay Detected is on and critical, and fires on the first check that sees it.

- Optional rules alert when STARTTLS is missing, when the server's IP has no matching reverse DNS (a common reason for rejected mail), or when connecting is slow.

## Example

After a mail server rebuild, the new config accepts relay from anywhere. The next SMTP check opens a critical incident, before spammers find the server and its IP ends up on blocklists.

Docs: [TCP](/docs/monitors/network#tcp) and [SMTP](/docs/monitors/email#smtp).

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Canonical page: https://watchfor.io/changelog/2026-05-10-tcp-smtp-monitoring · Site guide: https://watchfor.io/llms.txt