A month ago at the last IETF meeting, I talked to a bunch of email standards experts about the current wave of Internet email standards work. In these conversations I also built a mental picture of the previous waves.

Wave 1 was what really made email work over the Internet. The Simple Mail Transfer Protocol and the basic email message format were defined in 1982 with the major innovation of using domain names to find out where to deliver an email. This allowed email from one organization to reach an individual in another company. In 1989, this was somewhat updated with RFC1123, which made email addresses look the way they do today: mailbox@domain.example. Once mail got to the right server, POP (first described in RFC918 in 1984) allowed any mail client to look through the server’s queue of new mail and decide what to do with each message. Although that first POP was described so early, many did not use it in those years and it didn’t get much attention until POP3. Instead one would typically log into the SMTP server and look at its mailboxes there.

Wave 2 was POP3, IMAP and MIME, 1988 to 1994 or so. POP3 gained far more adoption than POP. IMAP defined a way to access the server-side repository for all one’s mail: not just the queue of new messages, but a hierarchy of mailboxes (called “folders” in many clients) which can be used to store mail for access by several clients. MIME brought Media to electronic mail: the ability to include image file formats, to use HTML instead of text, to attach Word documents and executables, and other variations necessary to business and eventually much beloved by spammers. MIME also introduced the very first non-ASCII characters in the body of email. MIME turned out to be big for other purposes too, like the Web.

There’s arguably a wave 2.5 or 3, adding security features from 1994 to 1999, including S/MIME, TLS support and authentication features for IMAP and SMTP. SASL was added to SMTP in 1999 although didn’t get put into IMAP until 2003. This mini-wave didn’t change peoples’ lives much except for those whose companies rolled out complicated and hard-to-use S/MIME infrastructures, but the continued deployment of IMAP and MIME over this period did change the email habits of many.

Today’s wave is starting to get complicated (oh, just starting? heh). It’s adding internationalization capability, step by painful step (to various IMAP functions, to various mail headers like an email Subject line, and most painfully, to email addresses themselves). It’s making IMAP and other mail infrastructure more usable by mobile clients (all the work of the Lemonade WG). It’s addressing security and spam, among other things new ways to sign messages (DKIM). There is also some refactoring and architectural work going on which may be very interesting in the long run — for example, features to assign URLs and attach metadata to IMAP messages. This kind of work already allows increasing innovation in how email clients can deal with mail (particularly mail overload and spam).

The people I work with today include:

  • Dave Crocker, who edited RFC822 (mail message format) in Wave 1
  • Joyce Reynolds, author of the first experimental version of POP, RFC918 in Wave 1
  • Mark Crispin, author of the first version of IMAP, RFC1064 in Wave 2, and other revisions of IMAP
  • Nathaniel Borenstein and Ned Freed, who did the first three versions of MIME, starting with RFC1341 in 1992
  • Marshall Rose, who updated POP many times (POP3 in RFC1081, RFC1225, RFC1460, RFC1725 and RFC1939) in Wave 2
  • Randy Gellens and Chris Newman, who have contributed significant updates to POP and IMAP in Wave 2
  • Paul Hoffman, who defined SMTP over TLS in RFC2487 in 1999, and who ran the Internet Mail Consortium
  • John Klensin and Pete Resnick, who edited the modern versions of SMTP and the Internet Message format (RFC2821 and RFC2822 respectively).
  • The same and many more participating in today’s wave, all of whom I greatly enjoy working with.

Of course, although talking to some of these guys helped me put together this picture of email standardization waves, any errors here are mine (and please let me know of errors so I can update this).