Okay thanks. I searched some more and I think that Spam Arrest's enterprise solution would also be an option for me. I forward my @mydomain.com e-mail addresses' email to my ISP and since Spam Arrest's enterprise solution would require me to update my domains' MX records to match with Spam Arrest's MX records I think this would do what I want (if I understand it correctly): I would be able to still receive e-mail even if my server would be down (am not really sure though), and I would have a nice option to reduce spam at the same time.
Does anyone have experience with Spam Arrest's enterprise solution?
http://www.spamarrest.com/enterprise/index.jsp