It seems to me that a good ISP would screen emails for viruses. This centralization would be much more effective, although it would add a bit of time to the transfer of mail, and the anti-virus software companies would lose much of their customer base. But wouldn't it be worth a few more dollars monthly to the average consumer? If they wanted to be really competitive, the ISP could offer this as a value-added service, rather than just the connection to the internet.

Am I missing something, or isn't this possible? I suggested this a couple of years ago to my own ISP, who remained remarkably silent on the subject.