What is an MX record?

How does an MX record work?

Every email address ends in a domain, and that domain’s MX records, published in its DNS, say where its mail goes. When a server has a message for someone at netflix.com, it asks DNS for the MX records of netflix.com and gets back a short list: the host name of each server that accepts mail for the domain, and a priority number for each host.

1. SendMail for name@netflix.comA server has a message to deliver
2. Ask DNSMX records of netflix.comOne host name and one priority per record
3. DeliverLowest number firstPreference 1 before 5, then 10 if no host answers

RFC 5321, the standard for moving mail between servers, sets the rules for reading that list:

• Lowest number first. Priority 1 is tried before priority 5, and 5 before 10. The numbers only rank the hosts; their size means nothing.
• Same number, shared load. When several hosts carry the same priority, the sender picks among them at random.
• Next number on failure. If no host at the top level answers, the sender moves down the list.
• No record, no list. A domain with no MX record is treated as if it named itself, and mail goes to the address the domain points to.

Netflix’s records follow the pattern exactly: one host at priority 1, two at 5, two at 10, all run by Google. Tesla publishes a single record. Both setups are normal. More hosts add fallbacks; the host names tell you who runs them.

Like every DNS record, an MX record also carries a time to live: how many seconds other servers may keep the answer in cache. That is why a change of email provider takes a while to reach every sender.

MX, SPF, DKIM and DMARC: what is the difference?

MX, SPF, DKIM and DMARC records all live in the same DNS zone, which is why they get mixed up. Only the MX record deals with mail coming in.

Record	DNS type	The question it answers	Direction
MX	MX	Which servers accept mail for this domain?	Incoming
SPF	TXT	Which servers may send mail for this domain?	Outgoing
DKIM	TXT, often reached through a CNAME	Did this domain sign the message, and is it unchanged?	Outgoing
DMARC	TXT	What should a receiver do with mail that fails those checks?	Outgoing

A missing SPF or DKIM record hurts the mail you send. A wrong MX record loses the mail you should receive, including replies to your campaigns.

Where do I find my MX record?

You find your MX record in three places: a DNS lookup shows what the rest of the internet sees now, your DNS host’s dashboard shows what you published, and your email provider’s admin console shows what you should publish.

1. A DNS lookup shows what the rest of the internet sees right now. From a terminal, dig MX netflix.com +short or nslookup -type=mx netflix.com returns each priority and host. On October 28, 2026, the first one returned these five lines, sorted here by priority:

   1 aspmx.l.google.com.
   5 alt1.aspmx.l.google.com.
   5 alt2.aspmx.l.google.com.
   10 aspmx2.googlemail.com.
   10 aspmx3.googlemail.com.

2. Your DNS host’s dashboard, at the registrar or DNS service that manages the domain, lists the records you published.

3. Your email provider’s admin console lists the records you should publish. Google Workspace and Microsoft 365 both show the exact values.

Web-based MX lookup tools run the same query as dig. If a lookup and your dashboard disagree, the change has not reached every server yet, or it was made somewhere else.

What does an MX record tell you about a company?

An MX record says more about a company than its few lines suggest, which is why sales and data teams read it.

• The email provider. Hosts under google.com or googlemail.com point to Google Workspace; hosts that end in mail.protection.outlook.com, or sit under mx.microsoft, point to Microsoft 365. It is one of the few pieces of technographic data that every domain makes public.
• A security layer. Hosts under pphosted.com (Proofpoint) or mimecast.com mean mail goes through a filtering gateway first, as at IBM and Forbes.
• Whether the domain takes mail at all. A null MX, a single record with priority 0 and the host “.”, declares that the domain accepts no email (RFC 7505). Every message sent there comes back as an email bounce.

What the record cannot tell you is whether a given mailbox exists. That takes a conversation with the server itself, which is where email verification happens, and where a catch-all email domain says yes to every address.

Which is which?

Five MX hosts, as real domains publish them. Which service receives the mail?

1. aspmx.l.google.com

2. smtp.google.com

3. tesla-com.mail.protection.outlook.com

4. mx0a-001b2d05.pphosted.com

5. us-smtp-inbound-1.mimecast.com

Show the answers

1. aspmx.l.google.comGoogle WorkspaceGoogle's own mail servers. Older Workspace setups list several aspmx hosts, as Netflix does.
2. smtp.google.comGoogle WorkspaceThe single MX value Google gives to the domains it sets up today, at priority 1.
3. tesla-com.mail.protection.outlook.comMicrosoft 365Exchange Online, the mail service of Microsoft 365, receives on hosts that end in mail.protection.outlook.com, named after the domain with its dot turned into a hyphen. Domains added since July 2026 get a host under mx.microsoft instead.
4. mx0a-001b2d05.pphosted.comSecurity gatewaypphosted.com is Proofpoint's hosted filtering service: it takes the mail first and passes clean messages on to the mailboxes.
5. us-smtp-inbound-1.mimecast.comSecurity gatewayMimecast filters inbound mail before delivery. The record names the gateway, never the mailbox provider behind it.

How do you look up MX records for a list of companies?

Looking up MX records one domain at a time is fine for a handful of companies; for a list, the records can come with the company record.

For a CRM, a target account list or an enrichment workflow, the MX records can come with the company record: Company Enrichment returns them in its mx field, each with its priority number and host, lowest number first and up to 10 per domain. The field is null when the domain has no MX data yet, and an empty list when the domain takes no mail, so a dead domain shows up before anyone writes to it.

Company Search works the other way around. It filters companies by the mail provider found in the MX records of their domains, from Google and Microsoft to security gateways, so a list of the Microsoft 365 companies in a segment takes one request.