[jenkings]

It sends an email when you have been unsubscribed containing the rss link, if you wanted to subscribe for another 90 days you can reply to the email and it should subcribe again.

I had initially set it to 30 days but that got annoying. Before I set it to 90 I was considering making it more intelligent as you mentioned, an exponential backoff retry mechanism, but then I decided I was overcomplicating things and the server usage is almost nothing at the moment. :)

As for your other question, it only sends what is available via the RSS feed, I've been considering adding the ability for it to pull in more content, but I think that would be a separate service, like an RSS proxy which created another RSS feed containing more contents, people could then subscribe via that link or the original. Maybe that already exists?