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Spam and virus filtering in the Classic Linux environment is done in two different places.
First, when incoming mail arrives via SMTP, any mail that either contains an identifiable virus (as diagnosed by clamd), or is spam with a high degree of certainty (as diagnosed by rspamd), is immediately rejected and never accepted. This is not under user control.
Second, any mail that is accepted, which might or might not be spam, is spam-filtered via SpamAssassin. This is under control of the user, and can be switched on or off via the Virtualmin control panel.