How often checking your email is normal? -- KM best practices

Here are some good reads, any suggestions are welcome:

                                           image courtesy: Apin Talisayon
• Study reveals how many times you should be checking email daily to reduce stress -- While the average person checks email 15 times a day, the study suggests three times is the right amount to keep added stress away.
• How Many Times A Day Should You Check Your Email?  -- 5 days a day...
• What I Learned From Checking Email Only Twice A Day
•  People either check email all the time, or barely at all
• The Science Behind Why Constantly Checking Your Email Is Making You Crazy
• A Quick Little Guide to Beating Your Email Addiction
• Sit back, relax and ignore your email inbox. Nobody expects you to read it all -- arbitrary limits, like checking email three times a day, will increasingly be the only way to cope.
• Hit the Pause Button on Your Email with Inbox Pause
• Managing your inbox efficiently - developing coping strategies. -- Remove pop-up alerts "You have 10 new email messages". These can be distracting and stop the flow of your current work. You could go all the way and only update your email inbox when you want to (rather than regular updates on every incoming email or time basis).