Mailfilter gateway & Secondary MX

[DKA]

Goodafternoon,
A lot of my customers would like to have a spamfilter/virusfilter before mails arrived on there own server, other customers would like to have webhosting on my server, and some customers would like to have secondairy mx (backup mx)

Like this:

mail ---> my spamfilter server (ispconfig) --> their mailserver
webhosting --> on my server (include e-mailboxes from customers)
mail ---> server1=offline --> server2 is backup --> server 1 (when online)

Actually I host websites on this machine, but I would like to sell all the services up here.
How can I configure my server so it can be also a spam filter gateway / webhostingserver and secondary mx server?

Is this possible on one machine with ispconfig?

[falko]

Regarding the secondary MX, take a look here: http://www.howtoforge.com/postfix_backup_mx

Regarding the spam filter: you can direct all MX records to the spam filter and then make the clients' mailserver fetch the emails from the spam filter with fetchmail or getmail.