I work in sales and also have customer emails, etc that I don't want to leave for too long. However I do think that you cannot be available for email 100% of the time... if you want to get anything done!
I have an email folder called @stack. Twice a day I copy everything from my inbox to @stack and then process them. What I try not to do is read/respond to every email as it plops into my inbox. I think this gives me a reasonable response time.
I also try to save time by not filing emails into folders (subject specific or whatever) but use Google Desktop to search for emails in @stack.
If I can do it in 2 minutes (ish) I do so; if it will take much longer I drag it to my Outlook Tasks where it goes into my Tasks inbox (task with no category).
If you are not careful (I've been there) you can just become "email driven" spending your whole day just reacting to emails as the pop up.
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Cheers
Mark
www.onwardandupward.org