I read this on GMail, and thought it would help to prevent email from being misidentified as spam. If you can build any other similar protections into your product, it would be very much appreciated! Here's their suggestions (the first one is the main thing):
Provide a 'List-Unsubscribe' header which points to a web form where the user can unsubscribe easily from future mailings.
All bulk messages you send must be formatted according to RFC 2822 SMTP standards and, if using HTML, w3.org standards.
Messages should indicate that they are bulk mail, using the 'Precedence: bulk' header field. (not sure about this one - thoughts? I'm afraid that could just force mail into spam folders that doesn't belong there)
Attempts to hide the true landing page for any web links in the message may result in non-delivery. (just a question about this - anyone have suggestions here for best practices? I use CamoLink on my server for shortening URLs, and I use WebAdverts for counting clicks on ads for my clients - that would fall under their rule I'm afraid)
Take care,
--Kyle