Email Domain Part Only Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching email domain part only, ported and verified for Python. Identity and credential patterns need both correctness and safety, since they're frequent targets for adversarial input. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Email Domain Part Only
# ReDoS-safe | RegexVault — Identity & PII > Email Address

import re

email_domain_part_only_pattern = re.compile(r'^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\.[a-zA-Z]{2,}$')

def validate_email_domain_part_only(value: str) -> bool:
    return bool(email_domain_part_only_pattern.fullmatch(value))

# Example
print(validate_email_domain_part_only("example.com"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Identity & PII > Email Address category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Domain labels are max 63 chars each. Total domain max is 253 chars. Underscores are not allowed in domain names (though common in hostnames). The TLD must be 2+ letters.