exim or postfix for an "unix-novice"?

hello, we have up and running a mac os x server 10.2.6. we use apples built-in software for filesharing and SMTP/IMAP (POP is deactivated). we have 2 mac os x clients and 5 windows clients (with office and outlook 2000). my colleagues are frustrated about spam and virus, so I would like to install spamassassin and clamav. you offer very good guides to install either postfix or exim, but I have 3 questions, that are not answered by your guides: - what app should be better for "unix-novices" like me to setup and maintain? - are both solutions independent of software updates? I mean, if I install on mac os x 10.2.6 postfix or exim and spamassassin/clamav and do later softwareupdates and security updates like 10.2.8, should work afterwards the whole mail-solution without manual modifications? - can I go back easily to apples own MTA? many thanks for your advice in advance! ferdinand