Best way to send email from my web app so it looks like it came from my users account

To: email@domain.com
Subject: [Test Blog] =?UTF-8?B?aGVsbA==?=
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
From:=?UTF-8?B?aGVsbA==?=<sender@senderdomain.com>
Message-Id: <20090207234737.39C9522802F3@web7.sat.wordpress.com>
Date: Sat,  7 Feb 2009 23:47:37 +0000 (UTC)
Return-Path: donotreply@wordpress.com

email.from = "From Name <fromemailaddress@example.com>";