One thing that worked for me is ALWAYS having an 'out of office' message on. The subject is 'I got your email'.
*Thank you for getting in touch.
I want you to know that your message has arrived safely. You are getting this response because I limit the time I spend on e-mail so that I can better focus on delivering great work to my clients.
I installed a program on my computer last year called RESCUE TIME and I learned that 56% of my week was spent on e-mail - wow! So I made a vow to change that. If you are interested in taking control of your own inbox and slavery to e-mail, I recommend this e-book: http://www.amazon.ca/Work-Smarter-Rule-Your-Email-ebook/dp/B00HXY5808.
To be productive I really only need to spend one hour per day on e-mail, it's tough but possible!
Have a great day and I'll get back to you soon - promise!*
This has stopped people expecting me to respond immediately, AND more importantly, has stopped me feeling guilty about not checking and responding every few minutes!
Hope that helps?