Any advice for a new server?

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Hi,

I have been running a mail server with sendmail/ MailScanner/ ClamAV/
Mailman/ Squirrelmail/ combo for the past 7 years.  It is now time to
migrate my accounts to a brand new server.  I was using Redhat9, but now
I'm 99% sure that I will go with Gentoo.  I am also 90% sure that I will
stay with sendmail/ ClamAV/ Squirrelmail and 100% sure to stay with
MailScanner/ Mailman. I don't have a whole lot of accounts so I do have
some room to make changes and play around.  Also, I just bought a new
copy of Julian's book, so I have allot of reading to to!  What I really
need is the ability to set up pop and web mail services for my clients,
also I need Mailman lists, and really good spam/ AV filters! Does
anybody have any advice for somebody starting with a fresh server? 

Thanks!
rick