From an external point of view, one doesn't see much difference between email and RSS feeds: both typically end up in your email client. The main visible differ

From an external point of view, one doesn't see much difference between email and RSS feeds: both typically end up in your email client. The main visible difference is that with a RSS feed you can retrieve older entries when you subscribe; it's funny how people associate RSS with news when one of its key features is to let you fetch old news. TinyLetter, btw, appears to offer this feature by letting the author resend old letters to new subscribers. An other difference is that one can reply to an email but not to a RSS feed. Reading the comments here it seems to me it is a key point relevant to TinyLetter versus Twittbook. TinyLetter is a one-way communication channel. Like a blog with comments disabled. This is to me a major feature for two reasons that are actually one: spam. With comments gone you don't have to deal with spam, trolls, etc. The second reason is "social interaction spam": when feedback is enabled, people may think they have to reply, support, "like", "retweet" etc. Often the reply is void of content. TinyLetter's key feature is that you are sending a "newsletter", making it clear that no feedback is required, which eliminates the social spam that pervades social networks.