Hi Roby,
yes, most smtp-mailservers do not require you to log in. However most servers don't accept sending mail from a different domain than you're logged in to and somehow you're logged in to some domain (or you wouldn't be on the internet)
Some servers require valid from addresses, most however do not. And it's not just your app that's offering this option to forge the sender, all (?) mail programs have options to set the sending name and address. It's not hard to trick people to believe that the sender is Bill Gates, or Kofi Annan, or the Pope if you wish. However, your IP-address will always show from where the mail was sent....
HTH
/Kejpa