citadel how to install antispam & antivirus?

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http://www.linuxquestions.org – i just installed citadel and everything is working great , but i m getting a lot spam. i had a pc with email zimbra emails server but it died. zimbra had antispam built in. so how can i do to do the same with citadel? plz some step by step. thank you all of you , in advance !!!!!!!!! ps: i have ubuntu 10.04 32bit server. (HowTos)