if you want the standard mailform content element in TYPO3 to send emails not from the ugly www-data@server.com sender but the writer´s email adress and name you just need to use explicitly labelled fields as follows:
- from_name
- from_email
This will do the trick. But there´s even more. If you need to provide a reply-to attribute you can do this by using these fields (which may be hidden):
- replyto_name
- replyto_from
Well, nowadays i´d recommend sophisticated mail form extensions like powermail but if you happen to edit a project that might help 
