[legitster]

This is a situation where you can save a lot of pain by bringing in outside help. It's not too hard if you have experience and know the limitations. But there are a LOT of gotchas. Even a simple poor choice of words can get the email caught in a spam filter.

If you have to white-knuckle it, I strongly recommend a service like Litmus or Email on Acid. They will also provide good templates to start from and good instructional content.