IMAP Enhancements in iPhone OS Update (iOS 4)

Apple's recent update to the iPhone operating system (iOS 4) contains some updates to the IMAP (the Internet Standard Internet Message Access Protocol) support. Details here. The RFCs now supported are:

  • COMPRESS (4978)
  • ESEARCH (4731)
  • CHUNKING (3030)
  • 8BITMIME (1652)
  • BINARYMIME (3030)
  • CONDSTORE (4551)

These standards are also supported by Apple's Mobile Me email service.

We have previously argued that mobile email will drive adoption of new IMAP standards, and in particular those defined in the LEMONADE Profile, described in Isode's white paper, "LEMONADE Profile: The Key Standard for Mobile Messaging."

This change has certainly not come as a revolution, but these developments in the iPhone suggest that these changes are coming gradually as an evolution and improvement. Support for two of these standards (both edited by Isode engineers) is of particular interest:

  • CONDSTORE (described in the white paper) is a complex specification that is key to fast reconnect, which we have not seen supported in an email client designed for a mobile device until now. Thunderbird 3 supports CONDSTORE.
  • ESEARCH (extended search) allows a client to efficiently search very large mailboxes. This is included in the second LEMONADE Profile, RFC 5550, and is not described in the white paper.

Since the LEMONADE work started, typical network bandwidth has increased significantly and so it is much easier to work without these extensions. However, use of these capabilities will improve performance for the end user, and differentiate iPhone email performance. LEMONADE capabilities will give a faster user experience, and will also reduce network traffic, which will improve battery performance and may reduce network usage charges.

We hope that this is the start of a trend for improved IMAP support in other email clients and mobile devices.

...Steve Kille. Steve is a periodic contributor to Ferris Research. He is also CEO of Isode, a messaging and directory server software vendor.

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