We are an ISP which are hosting Zimbra for SMB customers and we are currently looking for an external antispam solution which we can offer our customer as an extra service. Today we use Zimbra default values for antispam and we want to keep it that way to avoid adaptions and have as much as we can a homogeneous environment. For some of our customers the default zimbra antispam values is not enough so because of that we are looking into other solutions.

We are currently evaluating:

- Barracuda Spam & Virus Firewall 300Vx
Seems very effective, but we haven't found a good solutions for our customers with alot of alias, distributionlists and domain alias. Barracuda will then have 1 quarantine for each address and not an individual zimbra account. Or is it a solution for this we haven't seen yet?

- Mailstronghold for Zimbra.
I like that it is integrated to Zimbra, but how active and widely used is it?

- Proofpoint
Haven't started testing this one yet but at the first glance i'm wondering how the updating frequency works? I see that it is different proofpoint versions for each zimbra versions. So if we use proofpoint and want to update zimbra to latest version, we have to wait for proofpoint to release a new version?

So do any zimbra admins here have experiences with any of these or maybe other solutions that we haven't evaluated yet that you can recommend? All feedback will be much appreciated