Blog / Infrastructure

What Is an MX Record? Email DNS Explained

3 June 2026

An MX record (Mail Exchanger record) is the DNS entry that tells the internet which mail server receives email for your domain. When someone sends a message to you@yourdomain.com, their server looks up the MX record for yourdomain.com to find the delivery address. If you run several mail servers, each MX record carries a priority number that decides which one is tried first.

What an MX record does

DNS is the internet’s directory. Most people know it translates a domain name into an IP address, but it also stores specialised records for specific services. An MX record is one of those: it answers the question “where does email for this domain go?”

When a sending server has a message for you@yourdomain.com, it does not try to deliver to yourdomain.com directly. Instead it queries DNS for the MX record of that domain. The MX record returns a hostname — for example yourdomain-com.mail.protection.outlook.com for a Microsoft 365 mailbox. The sending server then resolves that hostname to an IP address and connects there to hand over the mail.

So an MX record never points straight at an IP. It points at a hostname, and that hostname has its own A or AAAA record. This indirection is deliberate: you can change which physical server handles your mail by editing one hostname, without touching every domain that points to it.

How MX priority works

A domain can list more than one MX record. Each one has a priority value — a number where lower means higher preference. The sending server tries the lowest-numbered server first.

MX record	Priority	Role
primary.mail.example.com	10	Tried first
backup.mail.example.com	20	Used only if primary is unreachable
backup2.mail.example.com	30	Last resort

If the primary at priority 10 accepts the connection, delivery happens there and the higher numbers are never used. They exist as fallbacks for outages. When two records share the same priority, sending servers spread mail across them roughly evenly, which is one way to balance load.

The numbers themselves are arbitrary; only their order matters. Priorities of 10 and 20 behave the same as 1 and 2. For most cold-email setups on a managed provider there is a single MX record at one priority, and you never touch it.

Receiving versus sending

This is the part that confuses people. MX records are about receiving mail, not sending it. An MX record tells other servers where to deliver mail addressed to your domain. It says nothing about whether mail from your domain is trusted.

Outbound trust is handled by three separate DNS records:

• SPF lists which servers are allowed to send for your domain.
• DKIM signs each message so the receiver can verify it was not tampered with.
• DMARC tells receivers what to do when SPF or DKIM fail.

You could, in theory, send cold email from a domain with no MX record at all. Outbound delivery would still work. But you would have no inbox to receive anything — and that breaks the loop cold email depends on.

Why cold email still needs MX

Cold email is not one-way. The whole point is to start a conversation, and several signals flow back to you that only arrive if your domain can receive mail:

• Replies. A prospect who responds emails your sending address. No MX record, no reply.
• Bounces. Non-delivery reports come back to the sender so you can clean your list. High bounce rates wreck reputation, and you cannot act on bounces you never receive.
• Unsubscribes and complaints. The Google and Yahoo bulk-sender requirements effective February 2024 expect you to honour unsubscribe requests and keep complaints low. Acting on those signals — and on any opt-out a prospect emails you directly — depends on a mailbox that can receive.
• Engagement signals. Replies are among the strongest positive signals for deliverability. A domain that cannot receive them looks suspicious.

Each sending domain you run should therefore have a real, monitored inbox behind a correct MX record. This is part of what people mean by cold email infrastructure: not just the ability to push mail out, but a complete, authenticated mailbox that can also take mail in.

Common MX mistakes

A few errors show up repeatedly:

• No MX record at all. Inbound mail bounces or vanishes. Replies and bounce reports are lost.
• MX pointing at an IP address. An MX record must name a hostname, never a bare IP. Pointing it at an IP is invalid and some receivers will reject it.
• Leftover records from a previous provider. Old MX entries that still resolve can send mail to a server you no longer control.
• Mismatched authentication. If your MX says one provider but your SPF and DKIM describe another, the picture looks inconsistent to receivers.

How Mailionaire approaches this

When Mailionaire provisions a sending domain, the full DNS layer — MX for inbound, plus SPF, DKIM and DMARC for outbound — is configured automatically on an isolated Microsoft 365 tenant, so every mailbox can both send and receive from day one. Billing is a flat $50 per active domain per month, with monitoring that replaces mailboxes and domains as they wear out. You can see exactly how the setup runs before any domain goes live.

FAQ

What is an MX record in simple terms?

An MX (Mail Exchanger) record is a DNS entry that names the mail server responsible for receiving email sent to your domain. When someone emails you@yourdomain.com, the sending server looks up the MX record for yourdomain.com to find where to deliver the message. Without a valid MX record, inbound mail has nowhere to go.

What does MX priority mean?

MX priority is a number set on each MX record that controls delivery order. The lowest number is tried first, so it acts as the primary server. Higher numbers are fallbacks used only if the primary cannot be reached. Equal numbers split delivery roughly evenly across servers.

Do I need an MX record to send cold email?

Sending and receiving are separate. SPF, DKIM, and DMARC govern whether your outbound mail is trusted; MX records govern inbound delivery. But cold email needs a working inbox to catch replies, bounces, and one-click unsubscribes, so a correct MX record is part of a complete setup.

Does a correct MX record make cold email legal?

No. An MX record is DNS plumbing, not legal permission. Whether you may send depends on the recipient's jurisdiction — Germany's UWG §7(2) generally requires prior opt-in for advertising email, including B2B. The sender stays responsible regardless of DNS configuration. This is not legal advice.

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