Public domains
When public_domain is true, how freemail providers are classified, and using the flag in B2B signup and lead routing.
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The public_domain field is true when the domain belongs to a consumer or freemail mailbox provider: Gmail, Outlook, Yahoo, iCloud, Proton free tiers, regional webmail hosts, and similar.
This is a classification signal, not a syntax error. [email protected] is valid and deliverable; the flag tells you the address is not hosted on the registrant's corporate domain.
Product teams use public_domain to:
EmailGuard maintains a curated provider list covering major consumer mailbox hosts worldwide, updated as new freemail services launch. Domains are tagged with stable provider labels you can use in analytics and routing rules.
| Signal | Overlap |
|---|---|
| Syntax validation | Required first; public check runs only when syntax passes |
| Role address | [email protected] can be both public and role |
| Relay domain | Relay services use their own domains (mozmail.com); not the same as public freemail |
| Disposable | Most freemail is not disposable; do not treat public_domain as throwaway |
Corporate Google Workspace addresses use custom domains ([email protected]); those return public_domain: false even though Google hosts the mailbox.
curl -sS \
-H "Authorization: Bearer YOUR_KEY" \
"https://emailguard.co/api/v1/emails/detect?email=alex%40gmail.com"{
"data": {
"email": "[email protected]",
"syntax_validation": true,
"public_domain": true,
"domain": "gmail.com"
}
}Work email:
{
"data": {
"email": "[email protected]",
"public_domain": false,
"domain": "acme.com"
}
}Mailbox provider classification is operational data, not defined by email RFCs. Address structure still follows RFC 5322. Domain names are compared after IDNA normalization.
| Use case | Typical rule |
|---|---|
| B2B only signup | Reject or waitlist when public_domain is true |
| Mixed B2B/B2C | Allow; use flag for analytics |
| Enterprise SSO | Often irrelevant once IdP owns identity |
Combine with normalized when deduplicating consumer signups that use subaddressing.