It is possible some hosted services have agreements with providers to stay out of the spam folder. These are services that have monthly and volume-related fees. ListMail is a "do-it-yourself" program that can be installed on the host(s) of your choice. Your reputation is up to you (and other clients on the same server) and your (or your hosts) relationship with the various providers. In my experience delivery can be quite good with shared hosting and especially with your own dedicated server (~$80/mo). It's important to have a host that is knowledgeable about email, polices their users, deals with spam complaints, monitors system mail logs for major/lengthy blocks, etc. This can be time consuming with unruly users, but the two
hosts I recommend have been around for some time and seem to be faring ok.
I think the best/only way to stay out of the spam folder is simply to receive and maintain a very low complaint-rate. With your own dedicated server, I believe it is also possible to contact hosts like Yahoo and have your email completely exempt from the spam folder. This is normally only an option if no other users/companies are using the same server.
Regards