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Help Centre

How to use helocheck, answers to common questions, and what the tool can and cannot do.

Getting Started

helocheck is a diagnostic tool that connects to a mail server, reads its SMTP greeting banner, and reports what the server advertises. It does what an admin would do by hand with a terminal — without needing a terminal.

  1. Go to the app page.
  2. Enter a mail server hostname. For example: mx.example.com, aspmx.l.google.com, or smtp.gmail.com.
  3. Select a port. The default is 25 (plain SMTP). 465 is SMTP over TLS (implicit TLS). 587 is SMTP with STARTTLS (submission port).
  4. Click Probe. The tool opens a real TCP connection, reads the server's banner, sends an EHLO command, and collects the capability list.
  5. Review the results: the server's identification banner, whether STARTTLS is offered, which authentication mechanisms are listed, and how long the handshake took. Click "What does this mean?" on any capability for an explanation.

That is it. There are no accounts to create, no configuration to set up, and no data is stored from one probe to the next.

Frequently Asked Questions

What does helocheck actually do?
It opens a raw TCP connection to a mail server on the port you specify, reads the SMTP greeting banner (the 220 line the server sends when you connect), then sends an EHLO command to see what the server advertises. It reports back: the banner text, whether STARTTLS is offered, which authentication mechanisms are listed, the raw EHLO capability list, and how long each step took. It does not log in, send an email, or store any data.
Why can't I just use a browser tool or a website checker?
SMTP is a line-based protocol over a raw TCP socket (port 25, 465, or 587). A browser cannot open a raw TCP socket. Cloudflare Workers and most other serverless platforms cannot open arbitrary outbound TCP connections. helocheck runs a real server process that speaks SMTP directly. This is a fundamental constraint — not a preference — and it is why the tool exists.
Which ports can I use, and why those three?
Port 25 — the standard SMTP port used for server-to-server relay. Port 465 — SMTP over TLS (implicit TLS from the start of the connection). Port 587 — SMTP submission port with STARTTLS (plain text then upgrade). These are the three IANA-assigned standard mail ports. The tool does not accept arbitrary ports to prevent scanning or enumeration.
What is STARTTLS and why should I care?
STARTTLS is an SMTP command that tells a client the server is willing to upgrade the plain-text connection to an encrypted TLS session. If a server does not advertise STARTTLS, your email could be sent in plain text over the internet. helocheck tells you whether the server offers STARTTLS — if it does not, that is worth investigating, especially for a submission or relay server.
What do the authentication mechanisms mean?
After STARTTLS, the server may advertise authentication mechanisms like AUTH PLAIN, AUTH LOGIN, CRAM-MD5, or XOAUTH2. These tell an email client what methods it can use to prove who it is. helocheck lists what the server advertises so you can verify it matches what your email client expects. It does not attempt authentication — it only reads the advertised list.
What does EHLO mean? I see it in the results.
EHLO (Extended HELO) is the modern SMTP command a client sends to introduce itself and ask the server to list its capabilities. The server responds with a list of supported features — STARTTLS, authentication mechanisms, message size limits, and more. The raw EHLO response is shown in the results panel. Each line is a capability the server advertises. This is the same output you would get by running openssl s_client -connect host:25 -starttls smtp and typing EHLO example.com.

Known Limitations

helocheck is a focused diagnostic tool. It is honest about what it does not do. Here is what is not yet built or deliberately out of scope:

No scheduled checks or monitoring
helocheck answers when you ask it. There are no cron jobs, no recurring probes, no email alerts, and no notifications. The tool does not send email. This is a deliberate design constraint, not a missing feature.
No user accounts or history
Each probe is independent. Results are shown in your browser and discarded when you navigate away. There is no database, no login, and no way to retrieve a previous probe. If you need to save a result, copy it before leaving the page.
Only three ports supported
The tool probes ports 25, 465, and 587 — the standard IANA-assigned mail ports. Arbitrary port probing is not supported to prevent network scanning or enumeration.
No authentication or login testing
helocheck reads the advertised authentication mechanisms. It does not attempt to log in, test credentials, or validate that authentication actually works. Never send credentials through this tool.
Pro plan and paid features are not yet available
The Professional plan (API access, bulk checks, STARTTLS upgrade testing, CSV export) is listed on the pricing page but is not yet built or purchasable. No payment processor is connected. The "Subscribe" button is disabled. When the Pro plan is ready, the site will be updated.
Server may block or rate-limit our IP
Some mail servers rate-limit connections from unknown IPs or block certain ranges. If a probe fails, the server may have rejected the connection. This is not a bug in helocheck — it is the server's behaviour being reported.
Only connects to publicly routable hosts
The tool connects from its server to the hostname you provide. It cannot probe servers on private networks, behind NAT, or on localhost. The hostname must be resolvable via public DNS.

Contact Us

helocheck is a small tool. If you have a question, found a bug, or have a suggestion, here is how to reach us:

✉
Email
Send an email to the site owner. Responses are typically within a few business days. There is no automated ticket system — every message is read by a human.
⚙
Report a bug
If the tool returns an error or unexpected result, include the hostname you probed, the port, and the exact error message shown. This helps us reproduce and fix the issue.
This is a free tool with no SLA. Bugs and feature requests are reviewed when time permits. There is no legal entity, registered address, or phone number associated with this service at this time. If you need a guaranteed support response time, helocheck may not be suitable for your production infrastructure.