incrediBILL - 11:37 pm on Mar 19, 2012 (gmt 0)
An E-mail relay is not even in the same ball park as http traffic through port 80
If I can get access to any site I want via a port 80 proxy I can spam forms, spam blogs, spam forums, scrape or DDoS websites, and make the person with the open port look responsible so it's just as bad or worse than spam.
Shouldn't be wide open for anyone outside your network.
Could be exactly how some sites currently under attack are happening, perhaps its not a botnet, perhaps it's just someone using everyone open port 80 on the planet to appear to be a botnet.