Email provider lookup
Enter an address or a domain. We read its MX and SPF records and name who hosts the mailboxes and which services send mail for it.
The MX hostnames each provider uses
Every hosted mail service publishes the hostnames its customers point MX records at. Once you know the patterns, you can read a domain's provider straight off a MX lookup. The table lists the ones you'll see most.
| MX hostname contains | Provider | Kind |
|---|---|---|
| aspmx.l.google.com, smtp.google.com | Google Workspace | Mailbox host |
| mail.protection.outlook.com | Microsoft 365 | Mailbox host |
| olc.protection.outlook.com | Outlook.com, Hotmail | Mailbox host |
| yahoodns.net | Yahoo, AOL | Mailbox host |
| zoho.com, zoho.eu | Zoho Mail | Mailbox host |
| messagingengine.com | Fastmail | Mailbox host |
| protonmail.ch | Proton Mail | Mailbox host |
| mimecast.com | Mimecast | Security gateway |
| pphosted.com | Proofpoint | Security gateway |
| iphmx.com | Cisco Secure Email | Security gateway |
Host patterns as published by each provider, checked September 2026.
Why the provider decides how an address verifies
The mailbox host answers the verification check, so the host sets the rules. Each large provider behaves in its own way, and knowing the provider before you check a list tells you what results to expect.
Google Workspace and Microsoft 365 block verification probes from cloud addresses, and Microsoft answers inconsistently and throttles hard. Yahoo accepts every recipient during the SMTP conversation, then bounces later, so a Yahoo-hosted domain reads as catch-all.
A security gateway adds a layer. It answers for the mailbox host behind it, so its rules are the ones your check meets. Our provider guides cover how each major host answers.
Reading the SPF includes
Your SPF record is a list of every service allowed to send as your domain, so it doubles as a map of the tools a company runs. An include of servers.mcsv.net means Mailchimp. sendgrid.net means SendGrid, and _spf.salesforce.com means Salesforce.
Looking at your own domain? Check that every include is still a service you pay for. An old include costs one of your ten SPF lookups and still lets that service send as you. Our SPF checker counts the lookups each one adds.
Checking a whole list across providers
A B2B list usually mixes Google, Microsoft, gateways and small hosts, each with its own rules. ZapBounce checks every address with its own SMTP check on port 25 and labels each result valid, invalid, catch-all or unknown, so you see exactly which answers the provider gave.
Unknown results are never billed, and duplicates are removed free. Upload a CSV on the bulk verification page, or see pricing: 10,000 checks cost $25 and credits never expire.
Questions people ask
How can I tell which email provider a domain uses?
Look up the domain's MX records. The hostnames name the provider: aspmx.l.google.com is Google Workspace, anything ending mail.protection.outlook.com is Microsoft 365, and yahoodns.net is Yahoo. This tool reads the MX records and matches them for you.
Is this company on Google Workspace or Microsoft 365?
Enter the company's domain or any address at it. If the MX records point at Google or Microsoft, the result names the service directly. If they point at a filter such as Mimecast or Proofpoint, the real mailbox host sits behind it, and the SPF includes usually name it.
What does a security gateway in the MX records mean?
Mail reaches a filtering service first, which scans it and passes it to the real mailbox host. Mimecast, Proofpoint, Cisco and Barracuda all work this way. The gateway answers the SMTP conversation, so the mailbox host behind it is hidden from DNS.
Can I find out which email marketing tool a company uses?
Often, yes. A domain's SPF record lists the services allowed to send as it, through include: entries such as servers.mcsv.net for Mailchimp or sendgrid.net for SendGrid. The second panel of the result names every service it recognises.
Know the provider, then check the address
Verify any list across every provider, with 100 free checks every month and no card needed.