Pro move: type dmarc:yourdomain.com or blacklist:1.2.3.4 straight into the box — it switches tools for you.
About this tool. Connects to a mail server, reads its greeting banner, sends EHLO and lists what the server supports — including STARTTLS. our edge (like most clouds) can't open port 25, so we test the submission ports 587 and 465, which is what your own devices use to send mail.
How to read your smtp server test results
We connect to a mail server, read its greeting banner, send EHLO and list what it supports, including STARTTLS.
Our edge cannot use port 25, so we test the submission ports 587 and 465, the ones your own devices use to send mail. Point this at your sending or submission host, not a recipient's inbound MX.
Common problems and how to fix them
Your submission host fails the test
Confirm it listens on 587 or 465, that STARTTLS is offered on 587, and that no firewall blocks the port from the public internet.
Common questions.Which host should I test?
Your outbound or submission server (for example smtp.yourprovider.com), not a recipient domain. Recipient MX servers only accept mail on port 25, which clouds block.
Why can you not test port 25?
Cloud platforms, including ours, block outbound port 25 to prevent abuse. We test 587 and 465 instead, which is what mail clients use.