How to Find Which Provider Is Behind an MX Record or SPF Include
To find which provider handles a domain's email, read its MX records and match each host name to a provider. dig +short MX example.com lists them, for example 1 aspmx.l.google.com. The MX host decoder names the provider behind each host you paste and marks it as a mailbox provider, a security gateway or a forwarding service.
Step 1: get the MX hosts
Run the lookup on Mac or Linux:
dig +short MX example.com
On Windows: nslookup -type=mx example.com. For many domains at once, use the bulk MX lookup.
Step 2: paste them in
Paste hosts, one per line. A bare host, a line such as 10 aspmx.l.google.com. or a full DNS line all work. You can also paste an SPF record or its include: hosts, and each include is read as its own host.
Step 3: read the table
Each row shows the host, the provider, what kind of service it is and where it was found. The decoder matches the end of each host against the same provider rules as the email provider lookup. A few examples:
| Host | Provider |
|---|---|
aspmx.l.google.com |
Google Workspace |
mail.protection.outlook.com |
Microsoft 365 |
mx.zoho.com |
Zoho Mail |
SPF hosts are matched first against SPF rules, so spf.protection.outlook.com reads as Microsoft 365 and _spf.google.com as Google Workspace.
Mailbox provider, gateway or forwarder
The kind matters more than the name. A security gateway such as Proofpoint or Mimecast sits in front of the real mailbox and filters mail first, so the MX host names the gateway, not the provider holding the mailbox. A forwarding service such as Cloudflare Email Routing passes mail on to another inbox. To see Microsoft 365 behind a gateway, use the autodiscover check. For delivery to gateway-protected domains, see verifying emails behind security gateways, and for whole lists, the secure email gateway checker.
When a host is not recognised
It is probably a company's own mail server or a smaller provider. That is not an error and does not mean the domain cannot receive mail. MX record errors explained covers the cases where something really is wrong.
What this tool cannot do
- It matches host names against fixed rules and does not look anything up.
- Behind a gateway, the host names the gateway, not the mailbox provider.
- It says nothing about whether an address at the domain exists.
Check which addresses exist
Knowing the provider does not tell you which mailboxes are real. Upload your list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason, and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.
Decode your hosts now
Paste them into the MX host decoder.
Common questions
How do I find out who hosts a domain's email?
Look up its MX records with dig +short MX example.com, then match the host names to a provider. aspmx.l.google.com is Google Workspace and mail.protection.outlook.com is Microsoft 365. The MX host decoder does the matching.
Why does the MX show a gateway instead of the mailbox provider?
A security gateway such as Proofpoint or Mimecast sits in front of the mailbox and filters first, so the MX names the gateway.
Can it decode SPF include hosts?
Yes. Paste an SPF record or its include: hosts. spf.protection.outlook.com reads as Microsoft 365 and _spf.google.com as Google Workspace.
What if a host is not recognised?
It may be a company's own mail server or a smaller provider. That is not an error.
Does the decoder look anything up?
No. It matches host names against fixed rules, so it cannot see a domain's live records.
Check your list before you send
Real mailbox checks over SMTP, and nothing is sent to the address. Sign in with Google and your first 100 email checks are free, no card. Plans for bigger lists are on the pricing page.