A few weeks back, I opined that Newsletter publishers would be forced to convert from email to RSS. There are basically two flavors of newsletters: the ad-supported newsletter and the paid subscription newsletter (many publishers provide both). And we’re going to need some support from the news aggregators if either is to succeed.
Tim Bray has already started the discussion on counting subscribers. His proposal uses a hash of the subscriber’s email address as a unique identifier. That would also provide a mechanism for keeping the count correct when distributing over both email and RSS. And the ad-supported newsletter would live on.
The paid newsletter needs username and password support from the RSS aggregator. In the short term, the username and password could be added to the URL. But this has obvious security concerns and causes problems when readers share their subscription lists.