MX records are the least glamorous part of email DNS and one of the more useful things to check before a campaign. They govern receiving rather than sending, which is why senders often ignore them — and why a small amount of attention here removes an entire category of avoidable bounce.
What an MX record does
When a server has a message for [email protected], it queries DNS for the MX records of example.com to learn which servers accept mail for that domain. A typical result looks like this:
example.com. MX 10 mail1.example.com.
example.com. MX 20 mail2.example.com.The numbers are priorities, and lower is tried first. The sending server attempts mail1 and only falls back to mail2 if the first is unreachable. Equal priorities are used to spread load across servers of the same rank.
Records for a domain using a hosted provider usually point at that provider rather than at anything you run — Google Workspace, Microsoft 365 and similar all publish their own hostnames here.
Why senders should care
You are not responsible for anyone else's MX records. You are affected by them, in one specific way: a domain with no MX record cannot receive mail, so every address at that domain is a guaranteed hard bounce.
This happens more than people expect. Domains lapse, businesses close, someone mistypes a domain at signup, and lists collected years ago accumulate addresses at domains that no longer exist. Sending to them produces hard bounces, and hard bounce rate is one of the clearest signals mailbox providers use to judge whether a list was maintained — as covered in our guide to bounce handling.
An MX lookup during validation removes these before a single message is attempted. It is a cheap check that directly protects the metric providers watch.
What an MX check can and cannot tell you
It confirms the domain is configured to receive mail. It does not confirm that the specific mailbox exists — [email protected] passes an MX check comfortably, because gmail.com has excellent MX records.
So MX validation catches dead domains, not dead mailboxes. That is still worth having: dead domains are guaranteed bounces, while a plausible address at a live domain is at least worth attempting.
On Email.biz.pk this runs automatically when a CSV is uploaded, alongside syntax checking and deduplication, so rows at unreachable domains are reported before the campaign is queued.
Your own sending domain
Two points for the domains you send from.
First, if you are sending from a domain, it should generally be able to receive replies. A domain with no MX record that nonetheless sends mail is a mild negative signal, and more practically it means anyone replying to your campaign gets a bounce instead of reaching you. For cold outreach in particular, discarding replies is an unforced error.
Second, MX records are entirely separate from authentication. Having them says nothing about whether your SPF, DKIM and DMARC are configured — those are different records answering a different question. Our free checker reports on both together, so you can see the whole DNS picture for a domain in one place.