i've seen certain websites using adsense in their email campaigns.. is it against tos? if not, is there any procedure to do that?
you can use adsense in blog feed which is delivered via email also. However no direct paste the code thing. It is only for premium publishers.
not directly in email. for the feeds, you need to get it from the adsense admin, if it isn't there it means your location isn't yet on the rss feed adsense program, so you can't have them.