What Is an MX Record?
Also known as Mail Exchange record, Mail exchanger record
An MX record (Mail Exchange record) is a DNS record that tells sending servers which mail servers accept email for a domain. Each MX record has a priority number and a hostname. Lower numbers are tried first, and higher numbers act as backups. Without a valid MX record, a domain cannot reliably receive email, including replies.
MX Record explained
When someone emails you, their server looks up the MX records for your domain, picks the server with the lowest priority value and delivers there. If it is unavailable, it tries the next one. An MX record must point to a hostname, not an IP address, and that hostname should not be a CNAME. Google Workspace now uses a single record, smtp.google.com, while Microsoft 365 uses a hostname ending in mail.protection.outlook.com.
MX records control receiving, not sending. SPF, DKIM and DMARC handle sending authentication. Still, MX matters for outbound: a domain with no MX record looks unfinished to spam filters, cannot receive replies from prospects, and some verification tools and receiving servers treat a sending domain that cannot receive mail as suspicious.
For cold email, every secondary domain needs MX records pointing to the mailbox provider hosting its inboxes, so prospects can reply and bounce notifications come back. Email verification tools also rely on MX lookups to check whether a prospect's domain can receive mail at all, which is one of the first checks they run on every address.
MX Record example
Acme Inc buys tryacme.com for outbound and sets up Google Workspace mailboxes on it but forgets the MX record. Sending works, but prospects' replies bounce with an error. Adding one MX record pointing to smtp.google.com with priority 1 fixes it within an hour, and replies start landing in the inboxes.
Google Workspace:
Host: @ (example.com) Type: MX Priority: 1 Value: smtp.google.com
Microsoft 365:
Host: @ (example.com) Type: MX Priority: 0 Value: example-com.mail.protection.outlook.comHow to set up an MX record
Get values from your provider
Open your mailbox provider's domain setup page and copy the exact MX hostname and priority it gives for your domain.
Remove old MX records
Delete MX records left over from your registrar's default email or a previous provider, so mail does not split across servers.
Add the new records
In your DNS host, add an MX record on the root domain (@) with the provider's hostname and priority.
Wait and verify
Allow time for DNS changes to propagate, then use an MX lookup tool and your provider's verification check to confirm.
Send a test reply
Email the new address from an outside account and reply to it to confirm both receiving and sending work.
Common mistakes
- Pointing an MX record at an IP address instead of a hostname.
- Leaving the registrar's default MX records next to the new provider's, splitting incoming mail.
- Setting up mailboxes on a cold email domain without MX records, so replies bounce.
- Confusing MX records with SPF and expecting MX to authorize sending.
MX Record FAQ
Priority tells sending servers which mail server to try first. The lowest number has the highest preference. If that server is unreachable, senders try the next lowest. Records with equal priority share the load. With a single MX record, the exact number matters very little.
Strictly, no. Sending depends on your provider's servers and authentication like SPF and DKIM. But without MX you cannot receive replies, and a sending domain with no MX record can look suspicious to filters and verification tools. Every sending domain should have one.
Often minutes to a few hours, depending on the record's TTL and your DNS host. Some resolvers cache old values longer, so allow up to 48 hours in the worst case before assuming something is wrong.
Yes. Multiple MX records with different priorities provide failover, and records with equal priority spread incoming mail. All of them should point to the same provider's servers unless you deliberately run a backup mail service.