def _tag_email(email_address, tag):
    """Add a plus sign and the tag before the first at sign in the email

    Args:
      email_address (str): Email address tag is to be added to.
      tag (str): Tag to add after the plus sign before first at sign.

    Returns:
      str: Email with the tag added.
    """
    return email_address.replace('@', '+{}@'.format(tag), 1)