ESP checker
Paste a list of emails or domains and see how it splits between Google, Microsoft, security gateways and other providers.
42% Google, 33% Microsoft
Send from about 6 Google and 4 Outlook inboxes for every 10. 17% of the list sits behind a security gateway, so keep those emails plain. This is a sample list of 12 company domains. Paste yours above.
Your inbox mix
What to do
1 thing to handle before you send.Domains
12 domains, most rows first.Next
What the ESP checker does
Paste a list of email addresses or domains, up to 5,000 rows, or drop a CSV export. The checker reads each domain's MX records and sorts the list by who handles the mail:
- Google Workspace and Gmail, with MX hosts like smtp.google.com and aspmx.l.google.com.
- Microsoft 365 and Outlook.com, with MX hosts ending in mail.protection.outlook.com or mx.microsoft.
- Secure email gateways that filter mail before it reaches the mailbox, such as Proofpoint (pphosted.com), Mimecast (mimecast.com), Barracuda and Cisco (iphmx.com).
- Other providers and self-hosted servers.
It also flags freemail addresses like gmail.com, disposable domains, and domains with no working MX at all. Your list is parsed in the browser and only the domains are sent, never the addresses.
How to read the split
The split bar shows the share of your list on each provider, weighted by rows, so a domain with 40 contacts counts 40 times. The inbox mix under it turns the Google to Microsoft ratio into a number of sending inboxes: a list that's 60% Google and 40% Microsoft points to 6 Google and 4 Outlook inboxes for every 10.
Gateways deserve their own look. When a company routes mail through Proofpoint or Mimecast, the gateway decides first, and it runs its own content and reputation rules on top of the mailbox provider's. Lists heavy on gateways reward plain-text emails with few links.
Domains with no MX can't receive mail. Remove them before you send, because each one is a certain bounce.
Should you match your inboxes to the list?
A common practice in cold email is to send to Google recipients from Google inboxes and to Microsoft recipients from Microsoft inboxes. Neither provider documents it as a filter rule, so treat it as one input next to authentication, warmup and volume.
What the split tells you for certain is where your deliverability work should go. Gmail and Workspace recipients mean Google Postmaster Tools and Google's sender guidelines. Outlook and 365 recipients mean Microsoft's filtering, and for its consumer domains such as outlook.com and hotmail.com, Microsoft has required SPF, DKIM and DMARC since May 2025 from anyone sending more than 5,000 emails a day. Gateway-heavy lists mean clean content.
How the checker gets the answer
Every email domain publishes MX records that name the servers accepting its mail. The checker resolves those records, matches the hostnames against known providers, and dedupes domains first, so a list of 3,000 addresses at 400 companies takes 400 lookups.
It reads public DNS only. It never connects to a mailbox and never sends anything. The download adds the provider to each of your rows, built in your browser.