Wednesday, 24 September 2003
RSS and E-mail
Tim Bray wonders what the difference between an RSS feed delivered via HTTP and an e-mail folder (e.g., via IMAP) is; I’ve wondered the same thing myself. As far as I can tell;
Subscribing to an RSS feed is anonymous; no one can send you messages outside of the channels you’re subscribed to, and if one starts carrying content you don’t like, you can unsubscribe. With e-mail, once your address is out there, you can’t get it back.
RSS items are tightly bound to their channels; they come pre-categorised for your convenience. To categorise e-mail, you need to set up “rules,” “filters,” or “recipes.” This is annoying for the expert user, and nearly impossible for the novice. To me, this is actually the biggest difference.
RSS metadata is easily structured and extended, thanks to XML. E-mail headers aren’t so obviously so, although I don’t think this is a big issue, at least for now.
E-mail has a different distribution model; in most cases, mail is sent to designated intermediaries with one protocol (SMTP), while clients poll designated intermediaries using another protocol (IMAP or POP). The intermediaries provide some take responsibility for persisting and delivering the messages in e-mail. Meanwhile, most usage of RSS is over HTTP, and can therefore take advantage of HTTP’s facilities, like SSL, caching, authentication, Web indexing and so forth.