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MX lookup: find a domain's mail servers and check they answer

Enter a domain to list its MX (mail exchange) records from several locations, then check port 25 and blacklist status of each mail server on demand.

Examples: 300+ locations worldwide · results in about 10 seconds

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What an MX lookup shows

The mail exchange (MX) hosts a domain's DNS zone publishes for inbound mail, queried from several HostTracker locations at once.

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Why port 25 and blacklist status matter for delivery

A mail server that does not answer on TCP port 25, or that is listed on a DNS blacklist, can silently lose inbound mail even while its MX record still looks correct.

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A check tells you today. Monitoring tells you the day it changes

This is a one-time result. A DNS, Port or DNSBL monitor rechecks the same signals on a schedule and alerts you when one of them changes.

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Want the IP addresses behind a mail server checked against blacklists on a schedule instead of once? See DNS blacklist monitoring.

Key takeaways

  • This tool queries the MX (mail exchange) records of the domain you enter from several HostTracker locations and lists each distinct mail server host name that comes back.
  • It does not display the numeric priority value that orders multiple mail servers; only the host names and the locations that returned each one are shown.
  • For each mail server you can run two more checks on demand: a TCP port check against port 25, and a DNSBL (DNS-based blackhole list) lookup against the host.
  • Both on-demand checks are separate free instant checks and count toward the same anonymous limit as the MX lookup itself: 3 checks every 5 minutes before a captcha step is required.
  • It is free, needs no login and no credit card.

Frequently asked questions.

An MX (mail exchange) record is a DNS entry that names the mail server a domain wants inbound email delivered to. A domain can publish more than one, so that a sending server has somewhere to retry if the first one does not answer. This tool queries the domain's MX records from several HostTracker locations and lists each distinct mail server host name that comes back, with the locations that returned it.
Enter the domain above and run the lookup: every host in the "Mail server" column is one of the servers that receive the domain's email, and its "Seen from" list shows which locations returned it. From a terminal, dig MX example.com +short shows the same list together with each server's preference number.
No. The lookup lists the host name of every mail server the domain's MX records return, but not the numeric priority (preference) value that decides which one a sender tries first. Treat every row as one of the domain's mail servers, not a ranked list. Senders try the lowest number first and move to the next one when it does not answer, and they spread mail across hosts that share a number (RFC 5321).
Use dig on macOS or Linux and nslookup on Windows; both show the preference number the tool leaves out. Run dig MX example.com +short or nslookup -type=mx example.com. For a domain with two mail servers, dig prints lines like 10 mx1.example.com. and 20 mx2.example.com., where the number before each host is its preference. The real example.com answers 0 . instead, a null MX, because it accepts no mail.
Senders fall back to the domain's own A or AAAA address and try to deliver there - RFC 5321 calls this an implicit MX. A domain that wants no mail at all can publish a null MX, a single record pointing to "." (RFC 7505). This tool shows both cases as no mail servers found. If you did expect mail, the records were never created or were lost in a DNS provider move: add the MX records your email provider gives you, at the DNS provider the domain actually uses.
An MX change behaves like any other DNS change: resolvers keep the old answer until its TTL runs out, so for a while some senders deliver to your new mail provider and others to the old one. A lookup from your own computer cannot show this, because it only sees the copy your own resolver has cached. A host whose "Seen from" list is shorter than the others is the visible sign of that overlap.
As long as the old record's TTL, often 3,600 seconds (one hour), because resolvers keep serving the previous answer until it expires. Keep the old mail server accepting mail during that window, and run the lookup again until every host is seen from every location. A host seen from only some locations means resolvers there still cache the previous MX set.
After a switch, the hosts of your previous email provider may still appear next to the new ones in the "Mail server" column. That usually means the old MX records were not deleted. Delete them, or some senders keep delivering to a mailbox you no longer read. If an old host is listed at only some locations, resolvers there may still be serving the previous set until its TTL expires.
No. An MX record must name a host (RFC 1035). If an IP address appears in the "Mail server" column, the record was created with an address instead of a host name. Create an A record such as mail.example.com that holds the address, and point the MX record at that host name instead.
Other mail servers connect to port 25 over SMTP (Simple Mail Transfer Protocol) to hand off inbound mail. If it is closed or filtered, senders queue the message and retry for a while, then bounce it, usually with no DNS error to explain why. When the port 25 check says "Not answering", check that the host name resolves, the mail service runs, inbound TCP 25 is allowed and no country blocking covers a region. The port checker tests any host from 300+ locations.
DNSBL (DNS-based blackhole list) databases, also called RBLs, list IP addresses that sent spam, were compromised, or - on a shared IP - were damaged by a previous tenant. A listing has nothing to do with whether the MX record itself is correct. The blacklist checker runs the same lookup against any host or IP address. If a host is "Listed on" one or more lists, fix the cause first, then request removal on each list's own site.
It needs no signup and no credit card. The MX lookup itself is one instant check. The "Check port 25" and "Check blacklists" buttons each start one more, only when you click them. Anonymous visitors get 3 instant checks every 5 minutes before a captcha step is required, so clicking through several mail servers in a row can hit that limit - wait a few minutes and try again.

Part of HostTracker's website monitoring software.