I'm considering a few anti-spam hardware firewall solutions for some clients of mine such as the Barracuda and MailFoundry products (I'm a network consultant). I have several clients that are too small to afford these products and it seems software running on their PC is their only answer. However, they may access their mail from several PCs or their cell phones. In short, I am trying to find out if there is something I can run on a server or appliance, that would allow me to protect the email accounts for these different clients with different domains and email accounts, and offer it as a service to them. I could host it offsite.
-All have 3rd party hosted email although it would be nice to offer it to clients that have their own email servers too.
-Most have their own domain so I could use domain forwarding but again, it would be nice to offer it to individuals that might just have an ISP email address.
-I haven't had a lot of experience with the hardware appliances. Specs say they can handle multiple domains based on the model you select, but does that mean multiple domains for the same mailbox (aliasing) or could I handle mail for that many different companies?
-Most of what I've seen with an appliance is that the MX record forwards all mail to the appliance, then the client's pop settings point to the appliance for retrieval. If possible, it would be nice if the appliance could check the pop server and process anti-spam defense by deleting the junk before the clients d/l their messages without ever "hosting" the clients mail. I still haven't completely thought this through and not sure how it could be implemented but I know devices can tag messages for deleting or retrieval without downloading them first on a POP server.
-Low expense is key since the clients are small and I have barriers of entry for offereing this as a service. The appliances I've found have rather expensive annual fees to keep them updated which may or may not be avoidable.
Does anyone have a hardware solution or know of software (preferably open-source or cheaper than the appliances) or even another service that would meet these requirements and allow me to run it myself? I need pointing in the right direction first, then I'll follow up by opening more questions for more points on details. Thanks in advance!