I am using Virtualmin on Centos 6.6 and currently doing a lot of searching/reading on hardening my system. I only use Usermin for email and would like to ask if there is any need, security wise, to use dovecot and procmail in this situation. Are these linked to Spamassassin and Clam AV in the virtualmin setup?
Procmail is used for email delivery, and that would indeed be needed.
Dovecot is used for accessing email via POP and IMAP. I vaguely recall that Usermin uses IMAP by default, though I can’t recall for sure. You could always temporarily turn it off and see if Usermin still works.
Alternatively, you could also just use a firewall to block remote access to IMAP and POP, or have Dovecot only listen on 127.0.0.1.