What is the Maximum Length of a Valid Email Address?

Understanding email address length limits is crucial for developers and marketers. Here's everything you need to know about RFC specifications and practical considerations.

The Official RFC Standard

According to RFC 5321, which defines the SMTP protocol, the maximum total length of an email address is 320 characters. However, this is broken down into specific components:

• Local part (before the @): Maximum 64 characters
• Domain part (after the @): Maximum 255 characters
• Total length: 320 characters (64 + 1 for @ + 255)

Practical Considerations

While 320 characters is the technical limit, in practice, most email addresses are much shorter:

• The average email address is around 20-30 characters
• Most email systems work best with addresses under 254 characters
• Some older systems may have lower limits (128 or 256 characters)

Breaking Down the Components

Local Part (Username)

The local part is the section before the @ symbol. It has a maximum of 64 characters and can include:

• Letters (a-z, A-Z)
• Numbers (0-9)
• Special characters: . _ % + -
• Some systems allow quoted strings with more characters

Domain Part

The domain part comes after the @ symbol. It has a maximum of 255 characters and includes:

• The domain name (e.g., example.com)
• Subdomains (e.g., mail.example.com)
• Each label (between dots) can be up to 63 characters

Why This Matters for Email Marketing

Understanding email length limits is important when:

• Database Design: Allocate appropriate field lengths (we recommend VARCHAR(320) or VARCHAR(254))
• Form Validation: Set proper maxlength attributes on input fields
• Error Handling: Provide clear feedback when addresses exceed limits
• Data Import: Validate email lengths during bulk imports

Common Issues and Solutions

Issue: Email Too Long

If a user enters an email address that's too long:

• Display a clear error message
• Show the character count
• Suggest using a shorter email address

Issue: Database Truncation

If your database field is too short:

• Increase the VARCHAR length to at least 254 characters
• Consider using 320 for RFC compliance
• Migrate existing data carefully

Best Practices

1. Database Fields: Use VARCHAR(254) as a safe default
2. Form Validation: Set maxlength="254" on email inputs
3. Server Validation: Always validate on the backend as well
4. Error Messages: Be specific about why an email is invalid
5. Testing: Test with long email addresses during development

Example Validation Code

// JavaScript validation example
function validateEmailLength(email) {
  if (email.length > 254) {
    return 'Email address is too long (max 254 characters)';
  }

  const [local, domain] = email.split('@');

  if (local.length > 64) {
    return 'Email username is too long (max 64 characters)';
  }

  if (domain.length > 255) {
    return 'Email domain is too long (max 255 characters)';
  }

  return null; // Valid
}

Conclusion

While the RFC standard allows up to 320 characters for email addresses, most practical implementations use a 254-character limit. As a developer or marketer, it's best to design your systems to handle 254 characters safely, with proper validation and clear error messages for users.