> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vouch.expert/llms.txt
> Use this file to discover all available pages before exploring further.
# Syntax Validation
> RFC 5322 compliant email format validation
## 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.
## What It Checks
Syntax validation verifies these components:
The username portion before the @ symbol
Exactly one @ separator required
The domain portion after the @ symbol
Valid characters per RFC standards
## Common Validation Failures
```text theme={null}
userexample.com ❌
user@example.com ✓
```
```text theme={null}
user@name@example.com ❌
user@example.com ✓
```
```text theme={null}
user @example.com ❌
john doe@example.com ❌
user@example.com ✓
```
```text theme={null}
user@example ❌
user@example.com ✓
```
## API Response
```json theme={null}
{
"checks": {
"syntax": {
"pass": true,
"latency": 0.5
}
}
}
```
Whether the email syntax is valid
Check execution time in milliseconds
## Configuration
Always configure syntax validation to BLOCK. An email with invalid syntax cannot receive messages.
## Next Steps
Verify the domain can receive email
Block temporary email services