Glossary
Mail Exchanger (MX) — Deep Dive
A mail exchanger is the server responsible for receiving email on behalf of a domain, identified by its MX DNS record. When an email is sent to you@yourdomain.com, the sending server looks up the MX record for yourdomain.com to find the mail exchanger's hostname, then connects to it on port 25 to deliver the message. The mail exchanger hostname must have a valid A record and should have a PTR record for full deliverability compliance.
MX Record Requirements
- Must point to a hostname, never an IP
- Hostname must have an A record
- Should have a PTR record for the IP
- Priority value determines preference order
Multiple Mail Exchangers
Multiple MX records with different priorities provide redundancy. If the primary is down, sending servers try the next priority.
Inspect MX and DNS in one run
Open DNS Preflight →FAQ
What is a mail exchanger?
The server that receives email for a domain, identified by its MX record. Sending servers connect to it to deliver email.
Can an MX record point to an IP address?
No. MX records must point to a hostname (A record), not directly to an IP. This is an RFC requirement.
What happens if my mail exchanger is down?
Sending servers retry for up to 5 days. If you have multiple MX records, the next priority server is tried automatically.