When someone emails you@example.com, their server looks up the MX records for example.com and delivers to the host with the lowest priority number. If that host does not answer, it tries the next one. MX only covers receiving mail; sending is covered by SPF, DKIM and DMARC.
example.com MX 1 smtp.google.com
example.com MX 0 example-com.mail.protection.outlook.com
Why MX matters for cold email
- Replies need somewhere to land. A sending domain without MX records cannot receive replies, and a domain that sends but cannot receive looks suspicious to filters.
- Verifiers use MX. Email verification starts by checking that the address's domain has MX records; no MX usually means the address is invalid.
- MX tells you the provider. The MX host shows whether a prospect's company uses Google, Microsoft or another provider, which is useful for provider routing rules.
Common mistakes
Leaving old MX records from a previous provider, pointing MX at an IP address instead of a host name, and forgetting MX on a new secondary domain you bought for outreach are the usual ones. Each new sending domain needs MX records for the mailbox provider you use on it.
The domain email checker looks up MX for any domain alongside SPF, DKIM and DMARC. In ZicReach, domain checks cover MX for every sending domain, and campaigns can use routing rules by provider, for example Google mailboxes to Google recipients, from the AI Email Marketing settings.