How to Check the MX Hosts for Every Email Address on a List

To check the MX hosts for every address on an email list, query the MX records of the domain after the @ in each address in DNS, then check that each host resolves. The bulk email domain MX hosts checker does this for every address in a pasted list or CSV and gives each one a row.

The check reads the domain, not the mailbox.

Why check this on an email list

A null MX or a broken MX host means mail to every address at that domain will bounce, so the whole domain can come off the list at once. A list of thousands of addresses has far fewer unique domains, so one lookup per domain is cheap.

The by-hand way

1. Take the domain after the @, for example acme.example from sam@acme.example.
2. Query its MX records, for example dig MX acme.example.
3. Note the preference numbers: the lowest is the primary, higher ones are backups.
4. Check that each host has an A or AAAA record, and repeat for every unique domain.

For a plain list of domains, see explain MX priorities: primary and backup.

Step 1: paste the addresses

Paste addresses one per line, or upload a CSV. Only the unique domains are sent, never the mailbox names.

Step 2: run the check

Press Check MX hosts. MX queries and host lookups are made in DNS, from our server. Nothing is sent to the domains, and no mail is sent.

Step 3: read the result

Result	What it means
More than one MX host	Two or more hosts; roles are in the CSV
One MX host	A single host, which many hosted providers use
MX problem	A host is an alias, an IP address or doesn't resolve
Null MX: takes no mail	The domain says it accepts no mail
No MX records	None published; mail may fall back to an address record

The CSV carries the hosts and their count beside each email. Only addresses at a null MX domain are left out of the list handed on to the mailbox check.

What this check cannot do

• It checks the domain, not the mailbox.
• DNS only: no connection is made to a mail server.
• No MX records doesn't prove mail will bounce; RFC 5321 allows a fallback to an address record.
• Up to 100 unique domains a run without an account, 500 signed in.

To see which provider runs the mail, use the bulk email provider lookup.

Next: the rest of the list

For the addresses that remain, use the verify page: the first 100 checks are free with a Google sign-in, no card.

Try it now

Paste your list into the bulk email domain MX hosts checker at simpleverifier.com.