Hi Danillo,
Thanks very much for the beer!
You have not told me much about your installation. Is it on a development machine, a hosted server, a server under your direct control?
Running in Medium Trust?
What kind of smtp service are you using?
There are a lot of things that can be the problem.
On a dev machine, its possible (likely in fact) that the ISP is blocking smtp traffic on port 25.
Its possible the smtp server is locked down and will only allow certain ip addresses to relay, maybe the web server ip is not allowed.
Its possible the messages is being sent but blocked by spam filters. Some spam filters do a reverse dns lookup on the ip that sent the mail and it it doesn't match the ip of the mail server it rejects it.
Its possible there is a firewall blocking the sending of mail.
Its possible your host has additional restrictions on smtp so it may have to go throguh their own server.
Hope it helps,
Joe