Hi Montague, 

Cyren Zero-Hour Outbreak Detection adds protection in the earliest moments of malware outbreaks and continued protection as each new variant emerges. It is intended to catch only NEW malware or new variants of existing malware. This is why we recommend that it's used as a complement to conventional antivirus technology as an additional protection against zero-hour virus outbreaks. This is also why you might see staggering differences between what Cyren Zero-hour will catch versus ClamAV or Windows Defender. 

Please see this description from our Online Help: 

I hope you get some feedback from other administrators as well with their experience. I just wanted to share this piece of information for anyone who isn't aware.

This is also the order we check things in. 
-Defender
-Clam
-Cyren

-CommandLine AV checks

Also once we find something we stop checking. So when directly comparing them we need to keep that in mind. I could see value in maybe having it always scan with all the available options, THEN do the virus found action.

Thanks for the information, Andrea and Matt. We still have another few weeks to think about it.

Will there ever be a cooperative relationship between SmarterMail and Webroot? I have it on my email server and it appears to severely interfere with SM. That would be an excellent addition to the chain.