Six public DNS signals agents can use to verify emails and domains in one second

S_B_B_B_K · reddit · 2026-10-11

A practical playbook for agents doing outreach, signup screening or lead research: before acting on an email or domain, check six public signals that take about a second each. Key points:

MX records: missing or null MX means mail won't deliver; they also reveal the mail provider (Google Workspace, Microsoft 365), a handy lead-enrichment field
Domain age via RDAP: scam domains are days to weeks old; real companies are years old
Throwaway services: Mailinator/Guerrilla Mail are red flags for signups
Role addresses (sales@, info@): team inboxes, often filtered in signups
SPF/DMARC: p=reject means impersonation is blocked; domains without either are easy to spoof, which matters when trusting invoices or payment requests
Website reachability: a company domain with no site is unusual

Limitation: you can't reliably check whether a specific mailbox exists without probing the mail server, which is unreliable and frowned upon. The author demoed [email protected] vs a mailinator address and wrapped everything into an emaildomaincheck tool call returning lookslegitimate/risky/invalid with reasons.

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Six public DNS signals agents can use to verify emails and domains in one second

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