[SpamCop-List] Mail not getting through [OT]

[Ook]

This is slightly OT, but I don't know a better place to ask, and I'm betting
several of you can help.

If I send mail to a hotmail account, it never arrives. If I send mail to a
hotmail account *and* CC the mail to a non-hotmail account, it arrives in
both accounts. I tried it with OE on an XP box, and Thuderbird on a linux
box to eliminate OS or email client issues. It only happes with one specific
provider, which tells me that the problem is likely the provider. They claim
that there is no problem with their system. How would you troubleshoot a
problem like this? I think the problem is with the provider, but how do you
prove it? And is there a better forum to post a message like this?

- email to a hotmail account never arrives
- email to a hotmail account that is cc'd to a non-hotmail account arrives
in both accounts, including the hotmail account.
- not OS or email client specific.
- specific to one service provider only - does not happen with other
providers
- service provider denies anything wrong on their end