Technical•Reviewed by Deliverability Engineering•4 min read

MX Records

Mail Exchanger DNS Records (RFC 5321)

Definition:MX records are DNS settings that specify the mail server responsible for accepting incoming email messages on behalf of a domain name.

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Deliverability Impact
Critical
Implementation Time
5 mins
Pro Tip from the Trenches

Never send cold outbound emails from a domain that lacks receiving MX records. Anti-spam gateways perform a reverse MX check during SMTP handshake and reject emails from non-receiving sender domains.

Google Workspace MX DNS Records
yourdomain.com. IN MX 1 ASPMX.L.GOOGLE.COM.
yourdomain.com. IN MX 5 ALT1.ASPMX.L.GOOGLE.COM.
yourdomain.com. IN MX 5 ALT2.ASPMX.L.GOOGLE.COM.
yourdomain.com. IN MX 10 ALT3.ASPMX.L.GOOGLE.COM.
yourdomain.com. IN MX 10 ALT4.ASPMX.L.GOOGLE.COM.

Frequently Asked Questions about MX Records

Spam filters verify that the sending domain is a legitimate, functioning domain capable of receiving incoming email. Spammers often send from fake domains with no MX records.

Detailed Technical Breakdown

When an email is sent to `user@yourdomain.com`, the sending server queries DNS for the MX records of `yourdomain.com` to determine where to route the SMTP connection.

MX records include a priority number (e.g., 10, 20) directing servers to try primary and fallback mail servers in order.

In cold outreach, secondary sending domains must have valid MX records pointing to their Google Workspace or Microsoft 365 tenant so they can receive incoming prospect replies and bounce notifications.

Why it matters for Cold Email & Deliverability

Sending domains without valid MX records are instantly flagged and blocked by receiving spam filters as fraudulent or disposable domains.

Proper MX configuration is required to receive prospect replies and automated bounce notifications.

How to optimize MX Records

  1. Configure MX records pointing to your email provider (e.g., `ASPMX.L.GOOGLE.COM` for Google Workspace) immediately upon registering secondary domains.
  2. Verify MX record resolution using DNS propagation checkers (like WhatIsMyDNS or MXToolbox).
  3. Ensure MX records do not point to expired or misconfigured mail servers.
  4. Test sending a manual test email to the domain to verify incoming reply receipt.

Common MX Records Mistakes

  • Setting up secondary domains for cold sending but forgetting to configure MX records, causing receiving servers to reject all outgoing mail.
  • Having conflicting MX records from two different email providers configured on the same domain.
  • Entering incorrect priority values in DNS configuration panels.
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Related Terms

Cold Email Infrastructure
The technical architecture of secondary domains, DNS records, Google/Microsoft mailboxes, and IP pools configured specifically to send outbound outreach safely at scale.
DKIM
DKIM is an email authentication protocol that attaches a cryptographic digital signature to outgoing emails, proving to receiving servers that the message originated from your domain and was not altered in transit.
DMARC
DMARC is an email security protocol that builds upon SPF and DKIM, giving domain owners instructions on how receiving servers should treat emails that fail authentication.
SPF
SPF is an email authentication standard that allows domain owners to publish a public DNS TXT record specifying which mail servers and IP addresses are authorized to send email on behalf of their domain.