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What are MX records?

MX (Mail Exchange) records are DNS records that tell the internet where to deliver emails for a domain. When someone sends an email to hello@acme.com, the sending server looks up the MX records for acme.com to find out which mail server should receive the email. MX records are the postal address of the email world — they direct mail to the right destination.

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How MX records work

1

Email sent to hello@acme.com

The sending server needs to find out where to deliver the email.
2

DNS lookup

The server looks up MX records for acme.com and finds mail.acme.com with priority 10.
3

Delivery

The server connects to mail.acme.com and delivers the email.
An MX record has two parts:
PartDescriptionExample
Mail serverThe hostname that handles emailmail.acme.com
PriorityLower number = higher priority10

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Priority and failover

You can have multiple MX records with different priorities. The sending server tries the lowest number first:
PriorityMail serverRole
10mail1.acme.comPrimary — tried first
20mail2.acme.comBackup — tried if primary is unavailable
If the primary server is down, the sending server automatically tries the next one. This gives you redundancy.

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MX records and SendKit

When you add a domain in SendKit, we generate an MX record for the send subdomain:
FieldValue
TypeMX
Namesend.yourdomain.com
ValueProvided on your domain detail page
Priority10
TTL3600

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Why does SendKit need an MX record?

SendKit uses the MX record on the send subdomain for two critical purposes: 1. Bounce handling When an email can’t be delivered (invalid address, full mailbox, etc.), the recipient’s mail server sends a bounce notification back. The MX record tells it where to send that notification — back to SendKit, so we can:
  • Mark the email as bounced in your dashboard
  • Trigger the email.bounced webhook
  • Track your bounce rate
2. Complaint handling When a recipient marks your email as spam, their email provider sends a complaint notification (via feedback loops). The MX record ensures these complaints reach SendKit so we can:
  • Mark the contact as complained
  • Add them to the suppression list
  • Trigger the email.complained webhook
Without the MX record, you’d be sending emails blind — with no visibility into bounces or complaints.
The MX record is on the send subdomain only. It does not affect your root domain’s email delivery. Your regular email (Google Workspace, Outlook, etc.) is not impacted.

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MX records vs other DNS records

RecordPurpose in email
MXDirects where to deliver email (and bounce/complaint notifications)
SPFDeclares who can send email for the domain
DKIMSigns emails to prove authenticity
DMARCDefines policy for failed authentication
MX handles inbound email routing. SPF, DKIM, and DMARC handle outbound email authentication.

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Common MX issues

ProblemCauseFix
Bounces not trackedMX record missing or incorrectAdd the MX record from your SendKit domain detail page
MX record not foundWrong subdomain nameMake sure it’s on send.yourdomain.com, not your root domain
Conflicting MX recordsMultiple MX records on the same subdomainRemove any MX records on send.yourdomain.com that aren’t from SendKit

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FAQ

No. The MX record is on the send subdomain (e.g., send.acme.com), not your root domain. Your existing email delivery through Google Workspace, Outlook, or any other provider is completely unaffected.
That’s fine — SendKit’s MX record is on the send subdomain, which is separate from your root domain’s MX records. They don’t conflict.
Yes. The MX record is one of the three required DNS records for domain verification in SendKit (along with SPF and DKIM).