OT? Fetchmail and backup MX

[Ugo Bellavance]

Hi,

        This question is not totally related, so I'm not sure if I should post here or not.  Please redirect me if needed or write me off-list.

        Here is the situation:  

- I've got one MailScanner server (Fedora) as a Primary MX that scans mail and then send it to my Exchange server.  The MailScanner server is in a DMZ and Exchange in the LAN.

- With my web hosting, I have enough pop accounts to cover all my users, so I made this server my backup MX.

Now it becomes less clear.  I have no idea of how to setup a backup MX, so I can't tell if I can use my hoster's server as a regular backup MX server.  What I would want is that when my primary MX is down, mail goes to the backup MX and the backup MX tries to send the messages back to the primary once in a while. (this is, what I think, a regular use of a backup MX.  But does the Primary have to do anything to tell the backup mx that it is back online?

What happens in my case is that the messages are sometimes sent to the backup MX.  I don't know the cause but I guess it is impossible that a server can respond to all requests all the time.  But the messages stay on the backup MX (which is normal in a case of e-mail hosting), so I must use fetchmail to get any occasional message that goes to the backup MX.

It works very well, but when I use fetchmail, spam checks are not done because it comes from 127.0.0.1.  Maybe I could re-enable spam checks on 127.0.0.1 since I don't generate a lot of e-mail locally.  

Any idea about what I could do to make this work better?

I know I could always buy a MailHop Backup MX from dyndns.org, it is not expensive, but I prefer use my head than money to solve problems.

Thanks,

-- 
Ugo