Desktop Bulk-Emailer Suggestion?
I want to send email to a list of people at a certain interval without getting them detected as spam.
You might consider some kind of Groups application provided by a large, multi-national corporation.
If you are part of a large, multi-national corporation, and you follow the anti-spam laws, your email should get through. If you are part of a small organization, consider using Yahoo Groups, the Google equivalent, or similar group management application. Then you can be sure that your emails get through, at least to the end-user's spam filter, and that you can't shoot yourself in the legal foot by unwittingly sending unsolicited emails.
You want a proper mailing list manager then. Mailman is what you're looking for on the linux side. List management will help you prevent yourself actually being spam too.