As a software developers email has been around about as long as I've been doing development professionally. Managing email 10 years ago was much different than managing it now. When you might get at most 5-10 emails per day (per account) then it doesn't take that much to clean up old emails and find old emails.
One of the great things that Google did when they came out with Gmail was to give people more than enough space for email. While Microsoft (MSN) & Yahoo were giving 3-5mb, Google gave you 1gb. Fortunately now all mail providers have caught on and give users plenty of space, when means you don't have to delete anything, almost ever.
So where's the problem? It's two-fold, for one if you have an offline mailbox of your mail then it's going to be huge & eat up a lot of unnecessary space. Two: finding old email threads or contacts can be very difficult.
If you just page through all of your email and cherry pick email to delete then it will take you forever to make a decision about keeping one email as opposed to another. These steps are going to be faster to perform on the webmail client for your email providers as opposed to whatever client your normally use (OS X Mail or Exchange).
Step 1: Delete large groups of emails based on keywords
Here I've basically searched my inbox for mail with "Buzz from Scott White" as the subject. Skim this list to make sure no email got mismatched and then click the Select All button then Delete.
Repeat those steps until there's no mail left which you want to delete. Some other search phrases you can use to delete "Facebook", "Monster" (Monster.com), "LinkedIn", "Twitter" or any other site which sends you tons of email.
Email from distribution lists & user groups can accumulate really large, I will usually delete all of these often too because there are already archives of these on the distribution list servers.
Step 2: Unsubscribe & Refine Email Subscriptions From Websites
By this point you pretty much know which sites are cluttering your inbox, if you haven't already, visit the websites and change your preferences so that you only get email from them that is relevant to you.
Our choices & selections of websites and news change over the years and if you find you always delete all mail from a certain website then it's probably time to unsubscribe. Also consider using an News or RSS reader (which is already built into every email client) so that you don't get as much junk in your inbox (personally I prefer Google Reader for subscribing to RSS feeds).
Step 3: Going Forward Delete Unwanted Email Right Away
- If you aren't going to read it anyway, just delete it
- If action items from an email is complete and you don't need to prove it in more than 30 days then delete it too (remember, Gmail keeps your Trash for 30 days unless you purge it)
- If you just read the article from the email, delete it right away. It's easy to get out of the habit of keeping Inbox clean and it doesn't take long for it to become cluttered again