sending mail form asp.net without crendiatials

Dear All I have account in one website.. I have also given my mail address while registration.. In that website there is facility to send any content of that website to friend mentioning his email address.. my problem is that after sending anything how it seems to my friend that content has been sent from my mail as I have given only my email id there not my email password...even when my friend hit reply to that mail it comes to in my mail inbox please sugest how the all things happens

I discussed this point here http://forum.dotnetbyramesh.net/index.php?topic=305.0

but did not get answer