Help My newsletters are flagged as spam.

Use a service like MailChimp.com for your newsletters, but be careful - they will ban you if a lot of users flag you as spam.

One thing you can do to avoid being flagged is make sure the people actually want your newsletter - they signed up to your service at least semi-recently.

I'd also recommend subscribing to a dedicated mail service. There are dozens of variables that affect your mail delivery. You should read the postmark blog (http://blog.postmarkapp.com/) for a peek into those.

Do you have reverse dns records set up?