avoiding spam filters

I use a custom made, server based mass emailer to service my 30,000+ website members with newletters etc. I have always assumed that many of these emails will get caught by spam filters as I belive that they have some way to detect if the email was sent as part of a large group. Im looking for soemone to advise on how best to aviod this and other element of my emails (use of specific words normally associated with spam etc) that may be preventing the properly delivery of these opt in emails. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform linux, php