Hi Mark,
You don't seem to understand the issue. My hosting provider has literally hundreds of thousands of domains. The email gets funneled for all, I assume, except those paying for co-location, through their heavy-duty mailhost. manitu sees spam coming from that mailhost, and blocks EVERY EMAIL FROM EVERY DOMAIN that goes through it, even though none of the rest of us are running windows or spamming....
Its the same old "one size fits all" syndrome.
What I was suggesting, is can't you have a back-up plan. For example:-
(1) run your own mail server ?
(2) use something like Google which will automatically forward by SMTP and allow POP3 collection ?
Obviously I don't know your computer situation. It seems your present 'service' is not always reliable, so is there anything we can do to help you devise an alternative plan ?