We use Cyrus-imapd together with Postix to effect final delivery of email messages to our clients. The final delivery server is isolated from the internet via a firewall and only pre-authorized host addresses can connect. All user pickup and delivery email traffic is handled through separate Internet accessible hosts that may establish these connections. The Internet facing hosts have Postfix and Amavisd running configured with ClamAV and Spamassassin.

Is there anything to be gained by having Amavisd, ClamAV and Spamassassin running on the IMAP delivery box in addition to the public hosts?