I run a mail service for a particular community of users. This email system goes far beyond an occasional email to a basic mailing list - it is the fabric that holds the community together. I would like to place ads in these email messages to monetize the system so that it can continue to exist. Google Adsense does not appear to allow such use of their ads (in email). What other reasonable alternatives are there out there?
Don't sell your list short by letting an automated system feed ads to it. Be vigilant to only recommend products or services that will help your readers. They have given you their trust. For your and their best interest, protect it.
Your best bet is to get direct advertisers. Since you know so much about your audience and you can show that you have a high readership, this should be fairly easy to do.
If you don't want to go the route of direct (strongly recommend you do), you can offer affiliate products. You should be able to find some within your market's interest that are good.
check out chitika, adbrite, they are generally much more flexible than adsense. note that most ads are context-sensitive, so putting them in emails would generally not be optimal
Not sure its a good idea (you would have to A/B test) but you could make your newsletter a teaser and the full content in a web page that can have adwords on.