there's no real problem here since when you save it to your computer you can then excess it,
is it a web based e-mail account?, the problem is on their side then and nothing is up with your computer, so I wouldn't worry,
it simply requires you to have the file on your computer before you can open it,
try creating a new account with the provider or with another provider if this is really annoying you,
my lycos.co.uk e-mail account would not let me open an attachment at all, it just enlarged the attachment icon instead of opening it, I send the email to my mail.com account and it opened up fine, it is just misprogrammed coding or a bug.