There is often a false sense of urgency in checking email. A common tip from the gurus: Try to limit yourself to 2 or 3 times a day. However, most of us are more like rats in a lab, pressing the tab to feed ourselves little pellets of sustenance at repeated intervals all throughout the day (insert collective sigh here). (click on image for origin)
Process email in batches. Try a quick scan to see what are urgent or time sensitive. Open those first. Also, obviously look at the sender names. People you already recognize should come first, but try to ignore for now notes from known senders who send "fun forwards."
Any emails that are invitations to meetings, events, etc. should be replied to as soon as possible, and added by the email program to your calendar. Since I use Gmail, I usually need to copy the info into a calendar entry with cut and paste. Add email reminders to yourself if you like, with the option within the calendar.
Determine a reasonable-for-you threshold of retained email. Initially, my "magic" number was 500. If my email queue of emails, including read and unread tops 500, I will force myself to do a Clean up. (Note, I tend to keep many older emails related to prior PR jobs for clients. Your own magic number might be 30, but then you probably won't need these tips.) I feel a little guilty about this high number of retained and still-to-process emails, but considering I get about 75 emails a day, by no means large in today's plugged in society, this number works for me so far.
In Clean Up mode, when you identify a sender or key word that you know you can part with multiple emails from, do a search and look for obsolete or out dated emails and group-delete them.
When I get involved in Clean Up mode, I go through some of my older emails and convert any information they contain that may prove meaningful again in the future to either Word documents, or I copy and add contact information to my Gmail contacts.
Try to read and act on emails that require action right away. You may find some that are worth reading later on a slow time. Some that may be read later include newsletters.*
As I gotten more proactive about cleaning up emails, I've whittled down my target range to 400 messages. However, when I get lazy about regular maintenance, this number can bloat to 500, which is my threshold to schedule Clean up.
Either schedule or get in the habit of performing "clean up" sessions to review what you've stockpiled. (You can make it a bit of a game to see how many you can delete in a quarter of an hour, much like my mother had my brothers and sisters and I see how many toys we could pick up and put away in our rooms in a short period of time.)
Also, try to leave the perfectionist's tendency to need to review/save/archive or otherwise memorialize all information. Mostly, anything you receive via email you could actually live without revisiting ever again, without majorly affecting the quality of your life.
It's great to sign up for newsletters but I try to evaluate them on an ongoing base and unsubscribe if they are not continuing to deliver really helpful information.
Another observations...I recommend checking your email DRAFTS folder only at planned intervals to see what you have cached there. Sometimes an important message might be stowed there--out of sight, out of mind--that needs to be updated/finished and sent on to a recipient.
*Some newsletters I've found that are worth keeping:
Sarah Sevens Commentz
(since this post is soooo long already, and was supposed to be about brevity and streamlining, a complete list of my recommendations and links will be a later post!)