As soon as i see someone wanting to write an email package, I like to direct them to
NeoMail. No need to write it yourself. You can even embed NeoMail in an existing web app. NeoMail is cooler than Yahoo!, more organized than Outlook, and very user-friendly. I urge you to take a look. It will simplify your entire project as well as appease your worries (tried-and-true security and features). That is, unless you plan to rival NeoMail! :-O