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Overview

Syntax validation ensures the email address follows the proper format defined in RFC 5322 (Internet Message Format) and RFC 5321 (SMTP).
This is typically configured as a BLOCK check since an email with invalid syntax cannot receive messages.

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What It Checks

Syntax validation verifies these components:

Local Part

The username portion before the @ symbol

@ Symbol

Exactly one @ separator required

Domain Part

The domain portion after the @ symbol

Character Set

Valid characters per RFC standards

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Common Validation Failures

userexample.com ❌
[email protected] ✓

user @example.com ❌
john [email protected] ❌
[email protected] ✓

user@example ❌
[email protected] ✓

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API Response

{
  "checks": {
    "syntax": {
      "pass": true,
      "latency": 0.5
    }
  }
}
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pass
boolean
Whether the email syntax is valid
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latency
number
Check execution time in milliseconds

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Configuration

BLOCK

Always configure syntax validation to BLOCK. An email with invalid syntax cannot receive messages.

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Next Steps

MX Records

Verify the domain can receive email

Disposable Detection

Block temporary email services