email_validator.py

import re

def validate_email(email_address):
    email_address = email_address.split()
    # email address can start with any alphanumeric character.
    # username part i.e the part before the @ symbol cannot be more than 64 characters
    # domain part i.e the part after the @ symbol cannot be more than 251 characters
    # domain part can end with any of the following top level domain name (.com, .org, .net)
    pattern = re.compile(r"(?P<username>^[a-z0-9][\w.]{,63})@(?P<domain>[\w]{1,247}(.com|.net|.org)$)", flags=re.IGNORECASE|re.ASCII)
    if not pattern.match(email_address):
        raise ValueError('invalid email address')
    return true