Sending stops dead
A refused connection or failed handshake means staff cannot send, and the queue backs up fast.
Free Email Tool
SMTP Test
SMTP is the protocol your server uses to send mail. When it fails to connect, negotiate TLS or hand off a message, your email simply does not leave. This guide explains what a healthy SMTP conversation looks like — and a specialist will test yours for you, free. We never ask for your password.
Information:
Automated checker coming soon
What this tool checks
What a healthy SMTP connection looks like.
An SMTP test confirms your mail server can be reached and is willing to accept a message for sending. These are the parts that matter — none of which need your password.
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The server is reachable
The mail host should answer on its SMTP port (commonly 25, 465 or 587) with a healthy greeting.
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The right port responds
Submission (587) and SMTPS (465) are for sending; a blocked or wrong port is a frequent cause of "cannot send".
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TLS is offered and works
A healthy server advertises STARTTLS (or answers on an implicit-TLS port) so the connection can be encrypted.
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The handshake completes
The greeting, EHLO and TLS negotiation should all succeed before any mail is exchanged.
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It accepts a message
A working server accepts a properly addressed message for delivery rather than refusing it with an error.
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Errors are explainable
When it refuses, the SMTP response code points at the reason — relaying, authentication, rate limits or reputation.
Why it matters
If SMTP fails, nothing leaves the building.
MX records bring mail in; SMTP sends it out. When the sending path is broken, the impact is immediate and total — no outbound email at all.
TLS failures expose mail
If TLS cannot be negotiated, mail may travel unencrypted — or be rejected by receivers that now require it.
The cause is often subtle
A firewall change, an expired certificate or a port block can break sending without any obvious warning.
Common problems
The SMTP failures we see most.
Most "we cannot send email" calls trace back to one of these. A test pinpoints which — without ever needing your password.
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The submission port is blocked
A firewall or ISP blocks port 587 or 465, so the connection never even reaches the mail server.
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STARTTLS fails
A misconfigured or expired certificate stops TLS negotiating, and modern receivers refuse the unencrypted alternative.
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Relaying denied
The server refuses to send for the connecting client, often a configuration or authentication-policy issue.
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Rate limits or reputation blocks
The receiving side throttles or refuses the connection because of sending volume or a poor reputation.
Preview the checker
Test an SMTP server's connectivity
This is a preview of the automated SMTP test we are building. It checks connectivity only — it never asks for a password and does not run a live test or store anything you type.
Coming soon
Automated checking is on its way. A human audit is available now.
We are building instant, automated checkers as part of our Email Operations Center roadmap. Until then, a specialist will run this check by hand as part of a free Email Audit — and explain what it means for your business in plain English, with no jargon and no obligation.
- A real specialist reviews your setup — not an automated guess.
- Plain-English findings and the next step that actually matters.
- Free, with no obligation — we work alongside your existing IT.
Questions
Answers, in plain English.
What is SMTP, in plain English?
SMTP (Simple Mail Transfer Protocol) is the language mail servers use to send email to each other. When you click send, your server opens an SMTP conversation with the next server to hand the message along.
Which SMTP port should I use?
Port 587 (submission, with STARTTLS) is the modern standard for sending mail from a client; 465 (implicit TLS) is also common; 25 is mainly used for server-to-server delivery. A blocked or wrong port is one of the most frequent causes of sending failures.
Will this test ask for my email password?
No, never. This is a connectivity test that only needs a host and a port. A legitimate SMTP connectivity check never requires your password — anyone asking for one should be treated with suspicion.
What does a STARTTLS failure mean?
It means the server could not establish an encrypted TLS connection, often because of a misconfigured or expired certificate. Many receivers now require encryption, so a STARTTLS failure can stop mail going out — our TLS Checker guide covers the certificate side.
Does this tool run a live SMTP test?
Not yet — the automated test is in development. This page explains what a healthy SMTP connection looks like, and the form is a connectivity preview that does not run a live test. For results today, request a free manual audit.
Our staff suddenly cannot send email — can you help?
Yes. A total sending failure is usually a port, TLS or relaying issue we can isolate quickly. If it is urgent, request Emergency Email Support; otherwise a free audit will find the cause.