To send a mail, you need to know login, password and mail server that user is using. Then you need to authorize user and only after you can send email. Taking into account that some websites have captcha protection, you will need to take it into account too. So this approach is bad for feedback.
Another option is to send email is usage of web services that have API to send email. These services are often limited in amount of emails per day, might be banned in some servers and you will need to store credentials in game, so it might be stolen. This way is bad too.
You need to use another way for feedback. The easiest way I think is opening of browser with your website where players can send feedback (which can be send to your email using server-side).