Popular tools

Theme

MX Lookup

Check the MX records of any domain: its mail servers in delivery order, who runs them, their IPv4 and IPv6 addresses, and whether they answer with STARTTLS. Straight from the domain's own nameservers, beside Google's and Cloudflare's cached copies.

Sources: the domain's nameservers, reached from a root server · Google Public DNS · Cloudflare 1.1.1.1 · Team Cymru · mail servers tested from our server in Mumbai

Exactly the name you type: a www. or a subdomain is looked up as it is, never rewritten.

Try

What is an MX record?

An MX (mail exchange) record names the servers that receive email for a domain, each with a priority number: senders try the lowest number first.

When someone writes to name@airbnb.com, their mail server asks DNS for airbnb.com's MX records, picks the server with the lowest number and delivers over SMTP on port 25. The record holds a host name, never an IP address, and that name needs its own A or AAAA record: it may not be an alias (a CNAME, RFC 2181 §10.3).

An MX lookup reads those records and follows each server to its addresses, its network and the provider behind it. MX only steers incoming mail: who may send as the domain is SPF, DKIM and DMARC.

Anatomy of an MX recordairbnb.com, from its own nameserver
airbnb.com.Name300TTLINClassMXType1Priorityaspmx.l.google.com.Mail server (exchange)
Name · TTLThe domain that receives the mail, and how long caches may keep this answer: 300 s = 5 min.
PriorityLower is tried first. airbnb.com has 1, 5, 5, 10, 10.
Mail serverA host name with its own A and AAAA records: 192.178.211.27 and 2404:6800:4000:1025::1b.
1 aspmx.l.google.com.A host name with A and AAAA records
1 192.0.2.25An IP address isn't a valid exchange
1 mail → CNAMEThe exchange can't be an alias (RFC 2181 §10.3)
Every field as it comes from airbnb.com's own nameserver. The tool flags an MX that points to an IP address, a CNAME or a name with no address.

How to check MX records

Type the domain above and press Look up MX, or ask DNS from a terminal: dig example.com MX on macOS and Linux, nslookup -type=mx example.com on any system, or Resolve-DnsName example.com -Type MX in Windows PowerShell.

Each answer line is one server: the priority, then the host name. The number before IN is the TTL, the seconds a resolver may keep serving this copy. Add @ and a nameserver (dig @dns1.p08.nsone.net airbnb.com MX) to read the zone's own answer instead of a cache.

dig example.com MX +short

Each line: the priority, then the mail server. Add @ and a nameserver to skip caches.

Reading dig's answerrecorded 2026-10-23
bash · zsh
$ dig airbnb.com MX
;; ->>HEADER<<- opcode: QUERY, status: NOERROR1
;; flags: qr rd ra; QUERY: 1, ANSWER: 5

;; ANSWER SECTION:
airbnb.com.    3002  IN  MX   13 aspmx.l.google.com.4
airbnb.com.    300   IN  MX   5 alt1.aspmx.l.google.com.
airbnb.com.    300   IN  MX   5 alt2.aspmx.l.google.com.
airbnb.com.    300   IN  MX  10 alt3.aspmx.l.google.com.
airbnb.com.    300   IN  MX  10 alt4.aspmx.l.google.com.

;; SERVER: 8.8.8.8#53(8.8.8.8)5
  1. Status. NOERROR with answers. NXDOMAIN means the name doesn't exist; NOERROR with no answer means no MX.
  2. TTL. Seconds this copy may still be served: 300 at the source, counting down in caches.
  3. Priority. The order senders try, lowest first.
  4. Mail server. The host to connect to on port 25; the trailing dot ends the name.
  5. Who answered. 8.8.8.8 is a cache. @dns1.p08.nsone.net asks the zone itself.
The same five lines appear in the tool's Servers view, sorted and grouped by priority, with each server's addresses beside it.

How to read the result

The head says in one sentence who receives the domain's mail and how many servers stand behind it, with the provider's mark; the tinted rows below it are the findings that matter.

The Servers view lists every MX host by priority with its addresses, network and reverse DNS; the first server is tested on port 25 automatically and the others on request. On the right, the delivery path draws what a sender does with these answers.

MX lookup result: five MX records at Google Workspace, each mail server's addresses and STARTTLS test, and the delivery pathMX lookup result: five MX records at Google Workspace, each mail server's addresses and STARTTLS test, and the delivery pathThe verdictWho receives the mail, the servers and tiers, the network, the TTL and which nameserver answered.The serversEach MX host by priority with its IPv4 and IPv6 addresses, AS number and forward-confirmed PTR.The SMTP testSTARTTLS and the TLS version from our server on port 25; open a row for the whole conversation.The delivery pathSender, the shields on the first hop, each priority tier, then the mailboxes and their evidence.
An MX lookup of airbnb.com: the verdict, the servers in priority order with their addresses and STARTTLS test, and the path mail takes. Select a number to see what each part shows.

What does MX priority mean?

The priority (RFC 5321 calls it preference) sets the order: a sender tries the lowest number first and moves on only when that server doesn't answer or defers the message with a temporary 4xx reply.

Servers with the same number share the load: the sender picks one at random. Only the order counts, not the gaps, and 0 is a valid number. One MX record is enough when the name behind it spreads over many servers, as Microsoft 365's and Mimecast's do.

Our advice on backup MX: a backup at another company that filters less than your primary is a known spam path, and hosted providers already run redundant servers behind one MX name. If you keep one, it must apply the same SPF and spam checks as the primary (RFC 7208, Appendix F).

How a sender works through airbnb.com's five serverspriorities 1 · 5 · 10
Attempt 1priority 1
aspmx.l.google.comtried first, always
250 OK

only if it doesn't answer or replies 4xx

Attempt 2priority 5
alt1.aspmx.l.google.compicked at random · ½alt2.aspmx.l.google.comor this one · ½
equal numbers share the load

then

Attempt 3priority 10
alt3.aspmx.l.google.com½alt4.aspmx.l.google.com½
all fail: queue, retry for days
0 is validgithub.com publishes priority 0 for its only MX.
1, 5, 10 ≡ 10, 20, 30Only the order counts, not the gaps.
One MX can be enoughhp.com's one MX host stands for 6 addresses.
Senders move down the list only when a server doesn't answer or replies with a temporary error; when every server fails, the message waits in the queue and is retried for 4 to 5 days (RFC 5321).

Google Workspace MX records

New Google Workspace domains need a single MX record: smtp.google.com with priority 1. Domains set up before 2023 often still publish the five-record set that starts with aspmx.l.google.com; Google says both work and that a working setup needs no change.

The tool names Google Workspace for either set and marks the older one as legacy, never as an error. Pair the MX with SPF include:_spf.google.com and DKIM from the Admin console; Google allows up to 72 hours for new MX records to be seen everywhere.

The two Google Workspace setups, side by sidelive MX, 2026-10-23
Currentone recordrecommended
1 smtp.google.com.
Seen on google.comsendgrid.com
Legacyfive recordsstill valid
1 aspmx.l.google.com.5 alt1.aspmx.l.google.com.5 alt2.aspmx.l.google.com.10 alt3.aspmx.l.google.com.10 alt4.aspmx.l.google.com.
Seen on airbnb.comnytimes.comuber.comspotify.com
google.com's own MTA-STS policy accepts both:smtp.google.comaspmx.l.google.com*.aspmx.l.google.com
spotify.com still lists the older aspmx2–aspmx5.googlemail.com hosts at priority 10, seven records in all: extra legacy names do no harm.

Microsoft 365 MX records

Microsoft 365 gives each domain one MX record under mail.protection.outlook.com, such as microsoft-com.mail.protection.outlook.com, usually at priority 0. The first part is a token you copy from the Microsoft 365 admin center: it often looks like the domain with dashes, but not always.

Domains that turn on inbound SMTP DANE get a host under mx.microsoft instead, such as siemens-com.h-v1.mx.microsoft: that zone is signed with DNSSEC, so senders can check the server's certificate with DANE. While moving, both records are live, the new one first behind the old, then in front of it, until the old one is removed. Microsoft has no plans to sign mail.protection.outlook.com, so the legacy host isn't outdated.

Reading a Microsoft 365 MX hostmicrosoft.com · siemens.com
Exchange Onlinethe common form
microsoft-comtoken from the admin center.mail.protection.outlook.comExchange Online Protection
Seen on microsoft.comgithub.comunilever.com
With DANEDNSSEC-signed zoneDANE
siemens-comtoken from the admin center.h-v1a shard.mx.microsoftsigned zone
Seen on siemens.comshell.com
While moving to the new hostboth records live; the lower number wins
0contoso-com.o-v1.mx.microsoft.new · tried first
30contoso-com.mail.protection.outlook.com.old · until removed
One legacy host and one mx.microsoft host at different priorities is a migration in progress, Microsoft's documented steps, not an error: the tool says so instead of warning.

No MX record or null MX: what happens?

A domain without MX records can still receive mail: senders fall back to the domain's own A or AAAA address (RFC 5321 §5.1). Only a null MX, the single record 0 ., tells every sender that the domain accepts no mail (RFC 7505).

That makes the null MX the right record for a domain that never receives email: senders bounce at once, with 556 5.1.10, instead of retrying for days. Add v=spf1 -all and DMARC p=reject so no one can send as it either, as example.com does. MX records belong to one name: www.example.com doesn't inherit example.com's.

Four answers, four outcomeswhat a sender does with each
MX recordsairbnb.comDeliver to the servers in priority order.delivered250 OK
No MX, has A/AAAAwww.google.comDeliver to the name's own address: its A and AAAA records. If port 25 doesn't answer there, mail waits, then bounces.implicit MXRFC 5321 §5.1
Null MX: 0 .example.comDon't try at all. The sender bounces the message at once.refused556 5.1.10
Name doesn't existairbnb.cmoBounce: the root has no .cmo, so nothing under it exists.bounced5.1.2

A domain that sends and receives no mail:MX 0 .v=spf1 -all_dmarc p=reject

Each row is the tool's own verdict for that example: open it from the chips above the tool.

Mail not arriving? Where MX fits in troubleshooting

Read the bounce first: its status code says which step failed. MX problems show up as "host not found" or long delays; a missing mailbox is 5.1.1; authentication failures are 5.7.x rejections.

Work down the list: the domain must exist, its MX must name the provider you use, each MX host must resolve and answer on port 25, and only then do SPF, DKIM, DMARC and blacklists decide where a message lands.

From the bounce to the fixenhanced status codes, RFC 3463
Host or domain not found5.1.2 · NXDOMAINThe domain or its MX host doesn't exist. Check the spelling and the nameservers.DNS Lookup
Mail still goes to the old providerafter an MX changeCaches keep the old MX until its TTL runs out. Compare the zone with Google's and Cloudflare's copies.Copies view
Delayed, then bounced4.4.1 · no answer from hostThe MX host is down, has no address, or port 25 is blocked. Test the servers from our side.Test servers
User unknown5.1.1The MX works; the mailbox doesn't exist at the provider.Email Checker
Rejected: not authenticated5.7.1The receiver refused the sender. Fix SPF, DKIM and DMARC on the sending domain.SPF Checker
Blocked by address, or lands in spamlistedThe sending server's IP is on a blacklist.Blacklist Check
The two highlighted steps are this tool's own views; the rest open the matching tool.

MTA-STS, DANE and TLS for mail servers

Mail servers encrypt with STARTTLS only when both sides offer it, so someone on the path can strip the offer and read the message. MTA-STS and DANE let a domain demand TLS from senders.

MTA-STS publishes a policy over HTTPS (https://mta-sts.<domain>/.well-known/mta-sts.txt) listing the allowed MX hosts and a mode; with enforce, senders deliver only over valid TLS to those hosts (RFC 8461). DANE puts the server's key in a TLSA record at _25._tcp.<mx host>, which counts only where DNSSEC signs that zone (RFC 7672). TLS-RPT asks senders to report failures (RFC 8460). The tool checks that every live MX matches a policy mx: line.

Three locks on one hopa sender → proton.me, live
senderany mail server
STARTTLS · offered, TLS 1.3STARTTLS alone can be stripped on the way: 250-STARTTLS just disappears from the reply.
MTA-STS · enforcemx: mail.protonmail.ch · mx: mailsec.protonmail.ch · max_age: 604800 ✓ both live MX hosts match
DANE · TLSA 3 1 1_25._tcp.mail.protonmail.ch, signed by DNSSEC (protonmail.ch) ✓
mail.protonmail.chpriority 10
TLS-RPT is on too: v=TLSRPTv1; rua=https://reports.proton.me/reports/smtptls. The tool tests STARTTLS from our server; MTA-STS and DANE come from DNS and the policy file.

Popular providers' MX hosts

Most domains point their MX at one of a few dozen providers, and each publishes recognisable host names. That is how the tool names a domain's mail provider, and how you can check a setup against the provider's own values.

Gateways such as Mimecast, Proofpoint and Barracuda sit in front of the mailbox host; the tool then reads SPF and Autodiscover to name the likely mailboxes behind them.

MX hosts and SPF includes by provider16 of the 110+ providers the tool recognises
ProviderMX (priority host)SPF
Google Workspace1smtp.google.comor 1 aspmx.l.google.com + 4 altinclude:_spf.google.com
Microsoft 3650<token>.mail.protection.outlook.comor <token>.<x>-v1.mx.microsoftinclude:spf.protection.outlook.com
Zoho Mailregion in the TLD10mx.zoho.com20mx2.zoho.com · 50 mx3.zoho.cominclude:zohomail.com
Proton Mail10mail.protonmail.ch20mailsec.protonmail.chinclude:_spf.protonmail.ch
iCloud Mail10mx01.mail.icloud.com10mx02.mail.icloud.cominclude:icloud.com
Fastmail10in1-smtp.messagingengine.com20in2-smtp.messagingengine.cominclude:spf.messagingengine.com
Yandex 36010mx.yandex.netredirect=_spf.yandex.net
Titan Email10mx1.titan.email20mx2.titan.emailinclude:spf.titan.email
GoDaddy Professional Email0smtp.secureserver.net10mailstore1.secureserver.netinclude:secureserver.net
Namecheap Private Email10mx1.privateemail.com10mx2.privateemail.cominclude:spf.privateemail.com
Cloudflare Email Routingforwardingroute1/2/3.mx.cloudflare.netpriorities set per domaininclude:_spf.mx.cloudflare.net
Amazon SESshared with WorkMail10inbound-smtp.<region>.amazonaws.cominclude:amazonses.com
Mimecastgateway10<region>-smtp-inbound-1.mimecast.com10<region>-smtp-inbound-2.mimecast.cominclude:<region>._netblocks.mimecast.com
Proofpointgatewaymx0a-<id>.pphosted.com · mx0b-<id>or mx1-us1.ppe-hosted.com (Essentials)a:dispatch-us.ppe-hosted.com (Essentials)
Barracudagateway1<id>.ess.barracudanetworks.com10<id>.ess.barracudanetworks.cominclude:spf.ess.barracudanetworks.com
NAVER WORKSKorea10kr1-aspmx1.worksmobile.com20kr1-aspmx2.worksmobile.cominclude:spf.worksmobile.com

MX lookup: frequently asked questions

What is an MX lookup used for?

An MX record lookup shows which servers receive a domain's email and who runs them. Use it to see a company's mail provider, confirm an MX change after moving providers, debug bounces and delays, or check a domain before you send to it. This tool also tests each mail server's STARTTLS from our server and reads the domain's SPF, DMARC and MTA-STS.

How do I check MX records with nslookup?

Run nslookup -type=mx example.com. Each answer line shows the priority as "MX preference" and the server as "mail exchanger". Add a server at the end, such as nslookup -type=mx example.com 8.8.8.8, to ask a specific resolver, or name the domain's own nameserver to skip every cache. On macOS and Linux, dig example.com MX gives the same answer.

Can a domain have more than one MX record?

Yes. Each MX record names one mail server with a priority. Senders try the lowest number first, move to the next only when a server doesn't answer or defers, and pick at random among servers with the same number, which shares the load. gmail.com publishes five MX records at five priorities; yahoo.com publishes three at the same priority.

Can an MX record point to an IP address or a CNAME?

No. The MX value must be a host name that has its own A or AAAA record. An IP address isn't a valid value, and RFC 2181 forbids an MX host that is an alias (a CNAME). Some senders still follow a CNAME or connect to an IP while others refuse, so mail may arrive from some senders and bounce from others. The tool flags both.

How long do MX record changes take?

As long as the old record's TTL. Resolvers that cached the old MX keep using it until their copy expires, then ask the domain's nameservers again; a cached "no MX" answer expires the same way. Lower the TTL a day before you switch providers. Providers quote safety margins (Google allows up to 72 hours), and the Copies view shows when Google's and Cloudflare's copies refresh.

What is a null MX record?

A null MX is a single MX record with priority 0 and a lone dot as the host: 0 . (RFC 7505). It says the domain accepts no email, so senders bounce a message at once, with 556 5.1.10, instead of retrying for days. It must be the only MX record. example.com publishes one, with SPF -all and DMARC p=reject beside it.

What happens if a domain has no MX record?

Mail is still tried. With no MX record, senders deliver to the domain's own A or AAAA address, the implicit MX (RFC 5321 section 5.1). If nothing answers on port 25 there, the message waits in the sender's queue, retried for four to five days, then bounces. A domain that should receive no mail should publish a null MX instead.

Is a single MX record a problem?

No. One MX record is a complete setup when the name behind it is load-balanced: Google Workspace's smtp.google.com and Microsoft 365's mail.protection.outlook.com hosts each answer from many servers. RFC 5321 requires no minimum number of MX records. The tool shows how many IPv4 and IPv6 addresses stand behind each MX host, so you can see the redundancy.

Why does the MX show a different provider than I expected?

A gateway can sit in front of the mailboxes. Mimecast, Proofpoint, Barracuda and Cloudflare Email Security filter mail first, so the MX names the gateway while the mailboxes are at Microsoft 365, Google Workspace or another provider behind it. The tool reads the domain's SPF include and Autodiscover record to name the likely mailbox provider, and shows that evidence.

Are MX records public?

Yes. MX records are public DNS data by design: any mail server in the world must be able to look them up to deliver to your domain. They show which servers receive mail and who runs them, not who sends it or what is in the mailboxes. Hiding them would stop your email from arriving.

Do MX records affect sending email?

No. MX records only steer incoming mail to your servers. Which servers may send as your domain is decided by SPF, DKIM and DMARC, which receivers check on every message. You can send from one provider and receive at another; then both appear in SPF while only the receiving one is in MX.

Why can't I connect to port 25 from my computer?

Most home and mobile networks, and clouds such as AWS, Google Cloud and Azure, block outgoing connections to port 25 to stop spam, so telnet or openssl to a mail server times out. That says nothing about the server. This tool tests each mail server from our own server in Mumbai, which can reach port 25, and shows the whole conversation.

Missing something?Suggest a feature or a new tool

More DNS and email tools