[CentOS] mail server best practices question

Hello all,

About a year ago I set up a mail server on CentOS using this howto:
http://wanderingbarque.com/howtos/mailserver/mailserver.html
I managed to add amavisd-new with clamav and spamassassin.
It runs very well, but it runs on CentOS 5.2, and if I try to upgrade, 
amavisd-new and clamav break.
we are now also at the point where a backup mx will need to be implemented.

If necessary I am willing to implement a new mail server and a new 
backup mx.

What I would like to know is what solution you guys would recommend for 
the mail server and the backup MX?

Any pointers would be greatly appreciated.

Regards,
Coert