MX Lookup Explained: What MX Records Tell You About Email Deliverability

When email refuses to land in inboxes, the first place to look is rarely the email itself — it's DNS. Specifically, the MX records that tell the world where mail for a given domain should be delivered. Get them wrong and even a perfectly crafted message goes nowhere.

What an MX record actually is

MX stands for Mail Exchange. It's a DNS record that says: "if you want to send mail to anyone @example.com, hand it to this server." A domain can have multiple MX records, each with a priority number. Lower numbers mean higher priority — receivers try the lowest-numbered server first and fall back if it's unreachable.

A typical Google Workspace setup looks like this:

example.com.   IN   MX   1   aspmx.l.google.com.
example.com.   IN   MX   5   alt1.aspmx.l.google.com.
example.com.   IN   MX   5   alt2.aspmx.l.google.com.
example.com.   IN   MX   10  alt3.aspmx.l.google.com.
example.com.   IN   MX   10  alt4.aspmx.l.google.com.

Mail goes to aspmx.l.google.com first; if it's down, senders try alt1 and alt2, and so on.

What MX records tell you about a domain

You can learn a lot from a 30-second MX lookup:

• Does this domain accept email at all? No MX records = no inbound mail. Sending to it is guaranteed to bounce.
• Who hosts the mail? Hostnames ending in google.com mean Google Workspace. outlook.com or mail.protection.outlook.com means Microsoft 365. zoho.com, protonmail.ch, yandex.net — all giveaways.
• Is the company technical? Self-hosted MX records (using their own domain) usually indicate an in-house ops team, which matters for B2B targeting.

When MX lookups solve deliverability problems

Three common scenarios:

1. You're bouncing on a specific domain. Run an MX lookup. If there are no records, the prospect's domain is broken — remove from your list. If records exist but bounce continues, the mailbox itself probably doesn't exist (verify with an SMTP check).
2. You've been told your mail isn't arriving. Run an MX lookup on your own sending domain. Misconfigured MX records (e.g. CNAMEs where MX should be, missing priorities) can silently break receiving.
3. You're evaluating a prospect's tech stack. Their mail provider often hints at company size and budget.

Try our free MX lookup tool — paste a domain and see records, priorities, and the detected provider in under a second.

MX is one piece — pair it with SMTP verification

MX confirms the domain can receive mail. It doesn't confirm any specific mailbox exists. For that you need an SMTP-level mailbox check, which is what our bulk email verifier does for up to 10,000 addresses per upload — no SMTP knowledge required.