import re

def is_email(value):
    if not value:
        return False
    return bool(re.match(r'^[a-zA-Z0-9][a-zA-Z0-9._%+-]*[a-zA-Z0-9]@[a-zA-Z0-9][a-zA-Z0-9.-]*[a-zA-Z0-9]\.[a-zA-Z]{2,}$', value))