I stumbled across this Ferris Research article on measuring email response time and email SLA’s at Ferris Research. David Sengupta basically says that using email response time as a metric is a sure fire way to develop unproductive work habits in the organization:
“Being hyper-responsive to email around the clock suggests that you live an interrupt-driven work life and that you likely have a hard time concentrating for prolonged periods of time. Your overall productivity is likely to be reduced as a result, making you less valuable.
…
Many people are intensely productive but block hours or even days of email-free time, in order to focus on priority projects. When you hear managers or others in the company suggesting that there is some inherent value in someone’s ability to be instantly responsive to any message that comes their way, or in someone’s ability to process a massive amount of email, think again.”
This is, of course, exactly what we have been saying. Focus on your projects rather than your messages and you’ll be a lot more successful in the long run.