An MX record (mail exchanger) tells the internet which servers accept email for a domain. Without one, nobody can reply to you and many receivers treat your mail as suspicious.
What it looks like
Each MX record has a priority and a server name. Lower numbers are tried first. Google Workspace domains today use a single record: priority 1, server smtp.google.com.
Why it matters for cold email
- Replies need it. A sending domain with no MX record can't receive the answers your campaign is meant to get.
- Filters check it. A domain that sends but can't receive looks like a throwaway domain.
- It tells you who hosts a prospect's mail. A Gmail or Outlook MX shows which provider will judge your email. mailzy uses this to match each lead with a mailbox on the same provider where you have one.
Check yours
Use the free MX lookup to see a domain's MX records and which provider runs them.