Do you want to put adsense in your html newsletters? As I know, Adsense only allow advertisement on web pages with content, not by Emails. Also, it's hard to send mass newsletters by mail server. I found that smartphone app can do the magic, let your members browse your newsletters on app. But it's too troublesome to make my own app for both Android and iOS. I searched a while and find an new app, ThreeTZ OTP that allows developers/webmasters to push free sms to their own members who use the app. Since it's a free one time password tool, I can ask my users to download it as a CAPTCHA alertnative solution. For now, I can push my webpage with ThreeTZ developer panel as newsletters but much higher reach rate. Here is the page for webmaster http://www.threetz.com/developers/ My case: I have intergrated the app with my free classifieds: http://www.cathaylist.com Welcome to post free ads on my site, then you can see it. After you post a free ads with ThreeTZ free OTP APP on my free classifieds. If you use the same classifieds script as I am using now, pm me. I can give you the part of script I intergrated with.
As long your newsletter is hosted under your domain and you show ads there in my OPINION should be ok. But if you put your ads code inside email you will get busted.
The difference between email and app sms: Email: 1.mail or webmail software-> 2. browse email (Adsense forbid) -> 3. click a link on email to the webpage with Adsense ThreeTZ SMS: 1. Smartphone sms -> 2.Browse webpage with Adsense on ThreeTZ APP browser So, using free SMS APP as ThreeTZ can shorten the steps for users to see webpage with Adsense. Also SMS is more easier to reach users then emails. So, I can push SMS to my members who use ThreeTZ app as 2-step verification or CAPTCHA, then display webpage with Adsense on APP browser to them. So far, for APP niche, Adsense even offers Admob for apps that may have no content at all.