def validate_addresses(addresses):
    """Check that ``addresses`` can be joined in a single string.

    :param addresses: email addresses
    :rtype: list or tuple
    :raises: ValueError if ``addresses`` couldn't be joined

    """
    addresses = list(addresses)
    try:
        """, """.join(addresses)
    except TypeError:
        raise ValueError(
            """Email addresses couldn't be joined in a single string: %s
Hint: probably one of them is not a string"""
             % addresses)
