Who cares? Sign up for a bunch of newsletters that only are posted through mail and not added online as well. Just copy them and use them. Who will ever notice and if anyone does... Do they know that they have the copyright, do they have the energy to go to court, do they really care to take you to court for posting of mail content online? One can always state that it was given away for free and that you only used the content after the original mailer had used it so you haven't taken any news value from him/her regarding that. Also.. Make a disclaimer somewhere on your site saying that you're not the copyright owner of the material and that you only make reviews of newsletters or what ever you are going to use. At least I wouldn't care and it's kind of smart to get content like this cause every RSS is already posted online and you will get duplicates while using mails/newsletters that haven't been posted online you will get pretty much original content in the search engines eyes and that for free and as much as you possible ever can have use for and probably even more. If I have sent out an mail I wouldn't search on the net for it afterwards.
Still.. I did find a mail from me for some time ago where they had put up a wiki comparing my answer to another company where we are selling the similar services but to different prices. In my opinion that's all ok. It's a review of our services rather then copying our content and still it was out there with good keywords, product names etc etc.
