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MX Lookup: preference, TTL and SMTP

MX preference, TTL, IP, SMTP diagnostics and blacklist.

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Lists MX records by preference with A/AAAA, TTL and PTR. Open SMTP diagnostics or blacklist from each row.

Queries leave from this Linux server, not your ISP DNS. Free. Cached answers can differ for a short time.

What is in MX?

Lower preference is tried first. Equal values share load. SMTP Test is on demand.

Field Meaning Example
Preference Priority (lower first) 10, 20
Hostname MX exchange aspmx.l.google.com
IP / TTL A/AAAA + cache lifetime SMTP and RBL target
SMTP Test Banner, PTR, relay, STARTTLS Row button

What MX Lookup does

Like MXToolbox “mx:”: lists MX by preference with TTL and A/AAAA, plus PTR for IPv4. Delivery also needs working SMTP.

No MX means the domain cannot receive mail (normal for web-only sites). Row SMTP Test runs the same port-25 diagnostics as Mail Server Test; blacklist opens that IP.

Examples

Google
aspmx.l.google.comSeveral MX with rising preference.
Single MX
mail.example.com · 10A should point at the right IP.

Reading results

Empty A often means a bad exchange or missing glue. Missing AAAA is usually a warning only. SMTP Test checks connect time, banner match, FCrDNS, STARTTLS and open relay.

Frequently asked questions

What is priority?

Preference: lower number first. Rising values like 10 and 20 are failover paths.

No MX?

No SMTP receive for that domain. Expected on web-only domains.

Where is SMTP test?

The SMTP Test button on each result row, or the Mail Server Test page.

Prefix?

Type mxlookup:example.com in the super box.

What is null MX?

RFC 7505: MX “.” means the domain does not accept mail.

Is IPv6 required?

No. An MX with AAAA can receive from IPv6 senders.