The reason it's probably working for you is because you're connected to your isp network- and you're never leaving the actual network - which is why I always test with an email address like hotmail or my isp email - if that works, everything should.

What you need to do is contact your ISP and ask them for the mail settings - they may be specific to that machine that allows relay without worry of spam attacks. So the servers are configured to talk to each other.  Anonymous I don't think will work because most hosting companies worries about being black listed.

Your hosting provider should be able to give you an answer and it will be fixed straight away.

Nina Meiers