SMTP Server Test

The SMTP test finds a domain's highest-priority mail server (via its MX records), opens a real connection to it on port 25, reads the greeting banner, sends an EHLO, and reports which capabilities the server advertises — including whether it supports STARTTLS encryption. No email is ever sent.

Domain name

What do you want to look up?

Blacklist Look Up

Looks up whether this domain's IP address (or the IP address you entered) appears on common email blacklists (DNSBL) — being listed can cause outgoing mail to be rejected or sent to spam.

Also look up blacklist status when I run this search

How to use this tool

Pick a lookup type from the dropdown, or type a shortcut straight into the field — e.g. mx:example.com, all:example.com, spf:example.com, whois:example.com — and press Enter.
Enter a domain name (e.g. example.com), or an IP address for PTR and blacklist look ups.
Toggle "Also look up blacklist status" above to include a DNSBL look up alongside your search.
Your last 20 look ups are saved in the History panel so you can revisit them anytime.

Why it matters

MX records only say where mail should go — they can't tell you whether the server there actually answers. A mail server that resolves but refuses connections, greets incorrectly, or lacks STARTTLS will cause delivery failures or force mail to travel unencrypted. Note: many networks block outbound port 25, so a timeout from this tool can reflect the checking server's environment rather than the mail server itself.

Examples

A healthy server answers with a "220" greeting naming itself, then advertises extensions like STARTTLS, SIZE, and PIPELINING in its EHLO response.
A server without STARTTLS receives mail in plaintext — and makes an MTA-STS enforce policy impossible for the domain.
If the greeting names a different hostname than the MX record points at, reverse-DNS and HELO mismatches may be hurting the domain's sending reputation too.