MX Lookup Guide: How to Check and Fix Email Delivery Issues
When email stops arriving, the problem often traces back to a single misconfigured DNS record. An MX lookup shows you exactly which mail servers a domain uses, in what order, so you can spot the issue quickly. This guide explains how MX records work and walks through the most common mistakes that break email delivery.
What is an MX record?
An MX, or mail exchange, record tells the internet which mail servers accept email for a domain, and it assigns each one a priority number. A lower priority number means sending servers try that mail server first, while higher numbers act as backups if the primary server does not respond. A domain without any MX record generally cannot receive email at all, even when its website works perfectly.
What a healthy MX setup looks like
- At least one MX record that points to a mail server which actually accepts mail for the domain.
- The mail server hostname named in the MX record resolves to a valid IP address.
- The domain also publishes SPF and DMARC records, which authorise which servers may send mail on its behalf and greatly improve deliverability. Our DNS health check guide covers both in detail.
Common MX problems and how to spot them
No MX records at all
Run an MX lookup and if it returns nothing, the domain simply cannot receive email. This happens most often on a domain that only serves a website and was never set up for email, or on a domain where someone removed the MX records by mistake during a DNS migration.
MX records pointing to a dead host
This is one of the most common causes of silently failing email. It usually happens after switching email providers, for example moving from a hosting company's built in mail to Google Workspace or Microsoft 365, without removing the old MX record. Mail keeps routing toward a server that no longer exists or no longer accepts mail for that domain.
Incorrect priority order
If a backup mail server carries a lower priority number than the primary server, sending servers try the backup first. This does not always break delivery outright, but it can cause delays or route mail through a system that was only meant to catch overflow.
How to check and fix your MX records
Start with our free MX Lookup tool, which lists every MX record for a domain sorted by priority and resolves each mail server to its IP address. Compare the results against what your email provider's setup instructions specify. If you recently changed email providers and the old MX record still appears, log in to your DNS zone and remove it, then wait for propagation, which our DNS records guide explains can take up to 48 hours depending on the record's TTL.
Try it yourself
Check any domain's mail servers right now with the MX Lookup tool. For a complete email health check that also covers SPF and DMARC, run our DNS Health Checker, and if you suspect a deliverability problem tied to your sending IP, our reverse IP lookup guide explains how PTR records affect that too.
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