You cannot exclude "From" attribute in the header of an email because it's required.
Are you perhaps having a problem with something to do with something .NET related? Maybe you want to use your own "from" email address and just have a page where the user enters a value to use for the "To" email address and a value to use for the email's body?
In that case, your server side code would automatically enter an email address for the "From" value for them.... this seems rather straightforward.
For a quick reference on how to send an email check out
this article.