Gmail's best features are tucked away in its nooks and crannies. There are endless tricks for Google's email platform, which turned 10 this year, so we'll be sharing our favorites every week. Scroll down for our 20 essential pointers, then add your own in the comments.
Source: Google+ user Gmail

Mass Unsubscribe

Want to get rid of those newsletters for good? There's an "unsubscribe" button next to the sender's address in promotional emails. It's a great one-click solution for decluttering your inbox! Another tip for the newsletters that don't get the "unsubscribe" button: type "unsubscribe" into the search box, and you'll probably find every deal, discount, and event email notification you've ever signed up for. You can also select all (but make sure to click "select all conversations that match this search" too) to banish historic newsletters from your inbox for good. Unroll.me is a plug-in that can clean up your junk mail with just one click.

Is Someone Else Reading My Email?

If you've got a creeping suspicion that someone else is eyeing your inbox, check your "last account activity." In inbox view, scroll all the way down, and in the bottom right corner in tiny text, you'll see "Last account activity: X minutes ago." Click "Details," and Gmail will reveal exactly when each IP address accessed your account, plus what type of device they were using.
Default Reply All

Having to resend an email is the worst. If you're frequently part of mass emails, consider making "reply all" default. In Settings under the General tab, head to "Reply Behavior" and switch to "Reply All."
Select Multiple Messages

In Inbox view, holding down the Shift key while selecting messages will check multiple email threads at once.
Narrow Your Search

Typing in any of these operators will get you a more refined search.
To find messages matching keyword A or keyword B, type "OR" in all caps, for example: from:amy OR from:david.
Find specific types of files with "filename:" for example: filename:jpg.
Search messages within a certain period with "after:" and "before:" for example: after:2014/04/30 before:2014/05/06.
More here!

Multiple Inboxes

Confront yourself with unread emails first thing every morning by setting up multiple inboxes. With this feature, you'll see your unread emails in one inbox on top, and everything else on the bottom. Head to Settings under the Inbox tab, then select "Unread First" under the Inbox Type drop-down menu.
Read Gmail Offline

The most underrated feature in all of Gmail? Gmail Offline. It's a Chrome extension that allows you to read, respond to, search, and archive emails without an Internet connection.
Click on the gear icon (top right) > Settings, then click the Gmail Offline tab. You'll need to let the extension sync and download emails for a little while before you get offline. And don't worry — this extension doesn't take up any space on your hard drive.
Essential Keyboard Shortcuts

First things first: if you don't have keyboard shortcuts enabled, head to Settings, and under the General tab, turn keyboard shortcuts to "on." Once you have these enabled, just type one letter or a combination of letters to simplify everyday tasks. The ones you need to know are:
j to go to older messages
k to go to newer messages
e to archive
shift + # to trash
/ to type in the search bar
a to reply all
r to reply individually
Set Up Filters

Is a big-box retailer sending too many emails? If you don't want to see those emails show up in your inbox but would like to keep on receiving them (just in case): Select the message > More > Filter messages like these > Create filter with this search (you can add other keywords or filter out only messages with attachments, too) > Select Skip the Inbox (Archive It) and Apply the label (create a new label with the name of the company). Alternatively, you can set up emails from select friends and family to skip the inbox and be filtered into special labels.
Show Unread Messages in Tabs

Have no fewer than five tabs open at all times? You are a certified tab fiend. A Google Labs extension called "Unread message icon" shows you how many unread emails are in your inbox. It updates automatically so you don't have to keep opening your inbox — just glance quickly at the tab! Go to Settings > Labs tab > Enable "Unread message icon."

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