def METHOD_NAME(email):
    """
    Retrieves the CITI member ID associated with the given email address.
    Args:
        email (str): The email address to search for.
    Returns:
        The member ID as a string, or None if no matching member is found.
    """
    username = settings.CITI_USERNAME
    password = settings.CITI_PASSWORD
    payload = loader.render_to_string(
        'user/citi/get_inst_member_by_email.xml', {
            'username': username,
            'password': password,
            'email': email,
        }
    )
    root = send_request(xml_payload=payload)
    memberid = root.find('.//intMemberID')
    if memberid is None:
        return None
    return memberid.text