Email Validator & MX Checker

What Is Email Validation with MX Lookup

Email validation with MX (Mail Exchanger) lookup verifies that an email address is both syntactically correct and associated with a domain that can actually receive mail. While regex-based validation checks the format, MX lookup queries DNS to confirm that the domain has mail server records configured—providing a much stronger signal that the address is deliverable.

This two-layer approach catches issues that syntax checks miss: typo domains (gmial.com instead of gmail.com), expired domains with no mail infrastructure, and disposable email services. For organizations sending transactional emails, marketing campaigns, or security notifications, validating email addresses reduces bounce rates, protects sender reputation, and improves deliverability.

How Email Validation Works

Email validation involves multiple stages, each catching different classes of invalid addresses:

Stage 1 — Syntax validation: Checks that the address matches RFC 5321 format: a local part, the @ symbol, and a domain. The local part can include letters, numbers, dots, and certain special characters. The domain must be a valid hostname.

Stage 2 — Domain DNS lookup: Queries DNS for the domain's MX records. MX records specify which mail servers accept email for that domain, along with priority values. If no MX records exist, the validator falls back to checking for an A record (some domains accept mail on their primary host).

Stage 3 — MX record analysis: Evaluates the returned mail servers. Major providers like Google Workspace (aspmx.l.google.com), Microsoft 365 (*.mail.protection.outlook.com), and Zoho use recognizable MX patterns. Disposable email services and known spam domains can be flagged at this stage.

Common Use Cases

• Registration forms: Prevent users from signing up with invalid or disposable emails
• Email list hygiene: Clean marketing lists before campaigns to reduce bounce rates below 2%
• Security operations: Validate email addresses in phishing reports and incident response workflows
• Account recovery: Confirm that recovery email addresses are still deliverable
• B2B lead qualification: Verify that business email domains have active mail infrastructure

Best Practices

1. Always check MX records, not just syntax — A syntactically valid address on a domain with no mail servers is worthless
2. Handle timeouts gracefully — DNS lookups can be slow; set reasonable timeouts and cache results
3. Respect rate limits — Aggressive SMTP verification can get your IP blocklisted; use it sparingly
4. Update disposable email lists regularly — New disposable providers appear constantly; maintain an updated blocklist
5. Combine with double opt-in — Even validated addresses benefit from a confirmation email to verify ownership