def split_email(s, h):
    """Given a sender email s and a HELO domain h, create a valid tuple
    (l, d) local-part and domain-part.

    Examples:
    >>> split_email('', 'wayforward.net')
    ('postmaster', 'wayforward.net')

    >>> split_email('foo.com', 'wayforward.net')
    ('postmaster', 'foo.com')

    >>> split_email('terry@wayforward.net', 'optsw.com')
    ('terry', 'wayforward.net')
    """
    if not s:
        return 'postmaster', h
    else:
        parts = s.split('@', 1)
        if parts[0] == '':
            parts[0] = 'postmaster'
        if len(parts) == 2:
            return tuple(parts)
        else:
            return 'postmaster', s