When I went to declutter their email I would do it by page. I recommend starting on the last page. You are more apt to get rid of older emails and that is where they all are! I first check off all of the definite trash and delete it. Next I go through and check off every email that belongs in a group and put them in a folder. For example, I made a folder called "Coupons/Sales/Deals" for any sales flyer type email. Another called "Passwords and Confirmations". This is where all the confirmations and emails about password resets goes for future reference. I especially like putting password emails in there for websites that I frequently forget the passwords to. That folder is the first place I look when I forget. Confirmations can be anywhere from payment confirmations to flight confirmations. I recommend creating a separate folder for payments you make frequently like bills. I have a folder specifically for my student loan payment confirmations.
Recently I discovered the Sweep feature in my Hotmail account. You're email service may or may not have something similar. I have had the same email from Hotmail since I was about 8, so I don't know what other email services off. Sweep is a gem. I wish I had it while going through my parent's email. It would have made things go a lot quicker!
Some of the cool features of Sweep is that you can have emails from certain senders go directly into the folder you want. My sales flyers get sent directly to "Coupons/Sales/Deals" now and no longer clutter up my inbox. I am subscribed to get the daily Zits comic sent to my inbox every say so that now gets directly sent to the "Comics-Zits" folder. I can't even tell you how much it has helped out my everyday chore of cleaning out my inbox.
Now you may say that I just moved all of that digital clutter out of sight but it is still there. Well, that is another nice feature about Sweep. You can give emails an expiration date! Sales usually do not last over a week so I have those emails set to be automatically deleted once they turn 10 days old.
I challenge you to try it!