Feature Requests
Support for DomainKeys Identified Mail (DKIM) RFC 4871
DKIM uses public-key cryptography to allow the sender to electronically sign legitimate emails in a way that can be verified by recipients. Prominent email service providers implementing DKIM (or its slightly different predecessor, DomainKeys) include Yahoo and Gmail. Any mail from these domains should carry a DKIM signature, and if the recipient knows this, they can discard mail that hasn't been signed, or that has an invalid...
Attachment Quarantine
Option to quarantine specified attachments of emails for further inspection or release by the administrator (instead of dropping them entirely).
Direct ClamAV Anti-Virus Support
Add documentation and/or more direct binding to the free ClamAV anti-virus, including the phishing signatures.
Per Test Actions
Allow specifying a different action for every test, e.g. Reject for the SPF Test and Tag Subject for the Keyword Blacklist.