In fact, they are so effective, spammers are now trying to discredit them. They have been faking mailblocks as a source when they send out spam in an effort to get ISP's to block them as being a spammer themselves, and in some cases this is actually happening.
When we are home we can use comcast (our ISP) to send mail out, interesting as comcast is a much more likely actual source of spam.
In any event, I am not giving up on mailblocks. This more than anything else is a testament to how effective they are.
