Need Advice Delivering Email

One of the features I want for FollowOn is to deliver a weekly email update. I assumed it would be as easy as plugging into the SengGrid API and sending emails on their way. However, even in testing, it appeared my emails were getting blocked by Outlook.

I heard that Basecamp had success rolling their own and I am curious how other founders solve this common problem? I also heard going paid on SendGrid might work better but if I can avoid $30 a month just for email that would be great.

Thanks for the input!