Starting from the CWP version 0.9.6+ you have a new awesome Postfix Mail Server Manager (Re-Builder)
With a single click you can select additional Mail Server options and ReBuild your mail server according to your needs.

Location in the CWP.admin area
Left Menu --> Email --> Postfix Manager

- AntiSpam and AntiVirus Protection (Spamassassin and ClamAV are scanning all your incoming emails, this requires server with min. 1Gb of RAM).
- rDNS check (Drop all emails if no rDNS/PTR)
- Reject Unknown Hostname (Reject unless the hostname has valid DNS record, IGNORE as you could be blocked also)

AntiSpam and AntiVirus
It's possible that ClamAV Antivirus will work with 512MB RAM server but its recommended to have at least 1GB+ RAM.