I was looking at the events viewer and I noticed several warnings, that the smtp server failed to deliver a message to (IP address and domain) because they couldn't authenticate.
I checked the domains, and they are all portals in places such as Brazil, Korea, Poland and Latvia.
Of course I checked the security settings of my smtp service (I am running Windows server 2003) and it wouldn't allow to rely unauthenticated users (the default), but in any case, I required only local account users can use the service and then I stopped it since I don't use it at the moment
nobody annoys me more than spammers and the thought of them using my server just drove me nuts. they won't