Hi Justin (and all others on-list)
I understand your grounds for blocking outbound SMTP for your customers (especially those on dynamic IP connections). It probably will do good to block infected customers that are spewing spam all over the world.
However, considering the number of mobile workers out there who send email via their laptops to corporate SMTP servers, won't blocking outbound SMTP affect them?
Since these corporate types (I'm guessing here) are probably unaware of how to change their email client's SMTP configurations, chances are that blocking outbound SMTP will probably cause quite a lot of pain.
After all, there are also those who frequently move from place to place so they're going to have to keep changing SMTP servers every time they go to a new place that's on a different ISP.
Cheers -- ANG Kah Yik (bangky)