Introduction

Email validation may appear simple on the surface, but modern validation APIs combine multiple technical checks to deliver accurate results. Understanding how they work helps product teams make better implementation decisions and troubleshoot uncertain cases.

DNS & MX Record Inspection

The API first checks whether the domain exists and can receive mail. This involves querying:

• DNS records

• MX (Mail Exchange) records

• Domain status and TTL values

Domains without MX records are immediately classified as undeliverable.

SMTP Handshake Simulation

To confirm inbox existence, the system initiates a “handshake” with the mail server:

1. Connect to the remote server

2. Announce the sender

3. Request delivery validation

The server then responds, indicating whether the mailbox exists.

Disposable Domain Detection

APIs maintain continuously updated databases of disposable email providers.
When detected, the email is flagged as high-risk or temporary.

Catch-All Detection

Some domains accept all incoming mail.
The API runs additional logic to determine if the domain is “catch-all” and classifies it accordingly.

Risk Scoring

Modern APIs provide a score that predicts deliverability likelihood based on:

• Server response patterns

• Domain reputation

• Historical bounce data

• Behavioral signals

Why Results Sometimes Show “Unknown”

Servers often use:

• Anti-spam firewalls

• Greylisting

• Rate limits

• Delayed responses

These can prevent the API from verifying inbox-level accuracy.

Conclusion

Email validation APIs combine networking, reputation scoring, and pattern detection to deliver reliable results. By understanding the workflow, SaaS teams can better integrate and interpret validation outcomes.