Sorry, blocking port 25 is BS IMnsHO. It means you are running a shoddy service. Granted, a vast majority of people will not need this but as a tech that runs his own servers at an across town ISP, if port 25 was blocked so I could not send thru any of my servers I would dump that shitty ISP in a second.
Quit running open relays and you won't have this problem.
