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.
Unlock the full report
30-day free trial · cancel anytime
- {{ plan.maxTaskCount == null ? 'Unlimited' : plan.maxTaskCount }} monitored sites
- All check locations in the report
- TLS, headers & timing details
- Scheduled reports
- REST API access
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.
Find out moreWhy 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.
Find out moreA 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.
Find out moreWant the IP addresses behind a mail server checked against blacklists on a schedule instead of once? See DNS blacklist monitoring.
Common questions
What is an MX record?
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.
Why does my mail server need to answer on port 25?
Other mail servers connect to port 25 over SMTP (Simple Mail Transfer Protocol) to hand off inbound mail - it is the one port that matters for receiving email, separate from the ports mail clients use to send or read 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. Run the free port checker directly on a host to see open, closed or filtered from 300+ locations.
Why would a mail server end up on a blacklist?
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 free blacklist checker runs the same lookup directly against any host or IP address.
Does this tool show which mail server is tried first?
No. The lookup lists the host name of every mail server the domain's MX records return, but not the numeric priority value that decides which one a sender tries first. Every row is one of the domain's mail servers, not a ranked list.
How many checks can I run?
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.
Is this tool free?
Yes, it needs no signup and no credit card.
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.
Part of HostTracker's website monitoring software.