MX Record Checker
Understand how MX (Mail Exchange) DNS records route email and how checking them reveals a domain's mail provider.
What Is an MX Record?
An MX record (Mail Exchange record) is a type of DNS record that specifies the mail server responsible for accepting email messages on behalf of a domain. When someone sends an email to user@example.com, the sender's mail server performs a DNS lookup for the MX records of example.com. The response tells it where to deliver the message.
How MX Records Work
An MX record consists of two parts:
- Priority — a number that indicates the order of preference. Lower numbers represent higher priority. When multiple MX records exist, the sending server tries the lowest-priority number first.
- Hostname — the fully qualified domain name of the mail server that will receive the email.
For example, a domain using Google Workspace might publish these MX records:
- Priority 1:
aspmx.l.google.com - Priority 5:
alt1.aspmx.l.google.com - Priority 5:
alt2.aspmx.l.google.com - Priority 10:
alt3.aspmx.l.google.com - Priority 10:
alt4.aspmx.l.google.com
If the primary server (aspmx.l.google.com) is unavailable, the sender tries the next priority servers in order.
MX Records and Email Provider Identification
Each major email provider uses characteristic MX hostnames. By examining the MX records of a domain, you can identify which provider handles its email:
- Google — MX hosts ending in
google.comorgooglemail.com - Microsoft — MX hosts ending in
protection.outlook.comormail.onmicrosoft.com - Yahoo — MX hosts ending in
yahoodns.netoryahoo.com - Zoho — MX hosts ending in
zoho.com - ProtonMail — MX hosts ending in
protonmail.chorproton.me
The Email Provider Filter checks MX hostnames against these known suffixes to identify the provider.
When MX Records Are Not Enough
In some cases, MX records alone do not reveal the true provider. This happens when:
- Filtering services — Companies like Mimecast, Proofpoint, or Barracuda intercept incoming email for security scanning. Their MX records appear instead of the actual provider's. In these cases, the tool checks SPF records as a secondary identification method.
- Custom mail servers — Some organizations run their own mail servers, which won't match any known provider signature.
- Hybrid configurations — During migrations, domains may have MX records pointing to multiple providers.
What Happens When a Domain Has No MX Records
If a domain has no MX records, it cannot receive email. The Email Provider Filter marks all email addresses at that domain as invalid. Note that some domains publish a fallback A record at the domain apex, which technically allows email delivery per RFC 5321, but the tool treats the absence of MX records as a failure to keep results reliable.
How to Check MX Records
You can check MX records for any domain using the Email Provider Filter. Paste email addresses or upload a file, and the tool will query DNS for MX records on each unique domain, identify the provider, and sort the results. To check a single domain manually, you can also use command-line tools like dig or nslookup:
dig example.com MXnslookup -type=mx example.com
Related Resources
- What Is an MX Record? — beginner-friendly explanation
- Understanding MX Records for Business Email
- Email Provider Lookup — how provider identification works
- Email Domain Checker — full DNS record overview