If you just use webmaster@domain.com on your webpage, it will get harvested sooner or later. Even if it is harvested once, it will be sold over and over again, and the e-mail going to webmaster@domain.com is basically junk. If you generate a unique address for each visitor, if the address akhjasio@domain.com is harvested once and sold over and over, you can simply block that one address, and visitors you wrote down your address weeks ago will still have a non-blocked address. If by some chance the harvester and another visitor went to your web site using the same IP address, there's only a 1 in 256 chance that they'll get the same generated address. If you're still unsure about something, let me know what's not clear and I'll explain some more.