import re


def validate_email(email):
    """
    This function ensures that the string is a valid email address or not.
    :param email: String to validate.
    :return: Boolean
    """
    regex = '^[a-z0-9]+[\._]?[a-z0-9]+[@]\w+[.]\w{2,3}$'
    return re.search(regex,email)