The recovery time for a phone interruption is at least 15 minutes. The recovery interruption from an email interruptions is 64 seconds (they measured this by videotaping user sessions using VNC). 70% of users reacted to a new message indicator within 6 seconds of seeing it (almost as fast as a telephone call), 80% reacted within 2 minutes of seeing the indicator.

The frequency of e-mail interrupts is far higher than telephone interrupts (at least for their subjects), meaning that the 64 second recovery time is multiplied by the number of such interruptions.

The recommendations of the study are to turn off sound and pop up new mail alerts, and to change the e-mail checking interval to no less than every 45 minutes.

These are really good recommendations for general usage. Of course, there are times when you really need to buckle down, in which case I pick specific times to check mail, and exit from the mail reader after each session. There are other times, when you are e-mail centric, in which case, you can check the relevant mail folders more frequently. It would be nice to be able to set the poll frequency on a per folder basis...