IMAP 4 protocol extensions

Spiced Up

Article from ADMIN 14/2013

By Patrick Ben Koetter , By Kristian Kissling

A set of protocol extensions keeps the legacy IMAP 4 protocol usable, which also helps mobile clients. We present a healthful mix of useful extensions.

When the first version of the Internet Message Access Protocol 4 (IMAP 4) appeared in 1994, mobile phones looked more like bones you would give your dog than phones – and they couldn't do much more than bones either. Digital data trickled off the Internet through modems in homeopathic doses. The Universal Mobile Telecommunications System (UMTS) and mobile email clients did not even exist, and email was only tentatively gaining ground.

Growing Demand

To adapt IMAP 4 to modern demands, and especially mobile clients, the Network Working Group of the Internet Engineering Task Force enriched the IMAP protocol in a whole series of RFCs with extensions that give IMAP new features, but without disturbing clients and servers that use older versions.

Many of the protocol extensions are still at the proposal stage; the unofficial IMAP wiki [1] has a fairly comprehensive list (see Figure 1) if you are interested in finding out more. Some of these extensions are also part of the Lemonade (License to enhance message-oriented network access for diverse environments) profile. Under this umbrella, RFC 4550 [2] gathered more than 20 IMAP protocol extensions explicitly to improve communication with mobile clients.