为什么经验丰富的开发人员从不使用正则表达式进行电子邮件验证？

# these are all technically valid emails!
valid_emails = [
    '"very.unusual.@.unusual.com"',
    'admin@mailserver1',
    'user+tag@gmail.com',
    'postmaster@[123.123.123.123]'
]

def dangerous_regex_check(user_input):
    # this regex can destroy your server's performance
    evil_pattern = r'^(a+)+b$'
    return re.match(evil_pattern, user_input)

# just 30 characters can crash your system
malicious_input = 'a' * 30 + 'b'

def smart_email_check(email):
    """quick and dirty email sanity check"""
    return (
        email and 
        '@' in email and 
        '.' in email.split('@')[1] and
        len(email) <= 254  # email length limit
    )

def validate_email(email):
    if not basic_email_check(email):
        return false

    # send verification token
    token = generate_unique_token()
    send_verification_email(email, token)

    return true

class EmailValidator:
    @staticmethod
    def validate(email):
        """
        Smart email validation
        - Quick syntax check
        - Verify deliverability
        """
        try:
            # Use a smart library
            validate_email(
                email, 
                check_deliverability=True
            )
            return True
        except EmailInvalidError:
            return False