Maybe slightly OT, but I'm wondering if anyone has experience and/or can provide recommendations on any email content checking SMTP software or hardware appliances, specifically that work with Zimbra. When I say content checking I am not referring to Spam and virus checking; I'm more than happy with the amavisd, clamav, spamassassin setup with Zimbra. In fact, prior to moving to Zimbra we already had a similar setup on our Internet email gateway, and are actually continuing to use this setup. Basically, in this case I am referring to scanning messages for inappropriate language and potentially confidential information, both in the message and any attachments. We are currently using a piece of software called Message Inspector, which sits on its own server. This software was originally released from a company called Elron, which was bought out by a company called ZixCorp, who in turn were bought out by another company, and now the software is no longer supported.
The software needs to be able to scan all incoming, outgoing, and internal email messages. I'd love to find an open source solution, but so far Google searches haven't turned up anything; I don't know if it's the whole freedom of speech tie in with OS or what. Additionally, ideally the software would only be for the type of content checking that I'm looking for, and not Spam and virus checking. Why pay for something we wouldn't be using, although I guess another point of checking wouldn't be the worse thing in the world.
Any feedback would be appreciated.