Is IMAP IDLE the right solution

To facilitate push Email to mobile devices? I'm doubtful, here are the reasons:

First, IMAP IDLE relies on keeping the IMAP connection alive. Mobile devices are more likely than desktop clients to experience network errors and timeouts as they travel. And devices capable of both Wi-Fi and cellular, like Apple's iPhone, automatically switches from one network to the other, terminating the connection as they do so. I feel that a true push solution should not depend on a persistent connection.

Second, an IMAP IDLE session only monitors a single mailbox. If you need to watch multiple folders simultaneously (like if you use server-side filtering or subaddressing), you need multiple sessions. Is any client capable of that?

Third, maintaining the session not only drains the battery, of which mobile devices have limited amount, it also hogs the data channels so I don't think telcos like that idea very much.

Michael told me OMA-EMN uses sideband SMS for notification, so it's designed to be friendlier to battery and network operators compare to IMAP IDLE. But I've yet to come across a client that supports OMA-EMN.

Comments:

Nokia's recently released Series 60 devices have native mail clients that are OMA EMN compatible.
See http://www.nokia.com/A4297065

Posted by Michael on April 24, 2008 at 07:45 AM PDT #

While using SMS as a notification system works well (It's how RIM does it with their Blackberry devices) you have to remember that SMS is extremely costly to the individual. In the UK, a single SMS of 180chars will cost as much as 12p. In comparison, all UK providers now offer 'unlimited' (meaning anything from 500mb to more than 1gb) data a month for a low fee (around £5 - £8). As more and more people pick up these data tariffs for youtube, googlemaps and other web surfing, Imap Idle becomes effectively free. I cannot see EMN working unless the carriers have a sudden bout of generosity :)

Of course, the problem with Idle is exactly the same problem you will experience with an IM client, weather updates, RSS feeds (pushed feeds, that is) etc. so maybe the question is not 'how to cope with flaky IP connections' but 'how to provide a stable IP connection across multiple possibly unstable channels'.

Posted by Robert Goldsmith on July 21, 2008 at 07:45 AM PDT #

IMAP IDLE is by no means ideal. in particular, it is rather wasteful that you need one connection per folder. (it has been suggested to change the behaviour when no folder has been selected to remedy this problem). but an inactive connection does \*not\* cost much, neither when it comes to power consumption nor bandwidth usage. IMAP IDLE requires a keepalive packet every 20 minutes or so (too lazy to look it up), which can hardly be called onerous. even with 100 folders, it will be on the order of a megabyte per day, which typically is much less than what a single frontpage of a newspaper (not optimised for cellphones) pulls down. for a user like me, with hundredds of messages per day, it will obviously be much cheaper to use IMAP IDLE than some SMS based scheme.

Posted by Kjetil T. Homme on August 21, 2008 at 09:42 AM PDT #

@Robert Here in the US, regular SMS is equally expensive ($0.20/msg by AT&T) unless you buy an additional SMS package.

Does anyone know how much carriers charge for sideband SMS?

Will IPv6 handle roaming between Wi-Fi and GSM networks?

@Kjetil When I enable Push notification on my iPhone, battery life reduces by about 2/3 so in my experience there's a significant difference in power consumption. What type of phone do you use? What kind of battery life do you get with and without an always-on data connection?

Posted by Robert Chien on August 26, 2008 at 07:34 AM PDT #

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I currently live in San Francisco Bay Area. For the past seven years, I have been designing and building messaging solutions for Sun.

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