The Authenticated SMTP is already on. However, people get it in Spam folder, or Never receive it. Probably cause it's filtered out as Spam by their servers. So Authenticating with DKIM is another step to prevent this.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.