The solution: read receipts
Read receipts are more common than you might realize. Most major email platforms give you the option to request return/read receipts with email that you send. Some will also let you specify these receipts for every email you're composing.

Keep in mind, these requests only do half the job; the recipient can still decline, and you’ll never receive the receipt you’re hoping for. Some email platforms, including Gmail and Apple Mail do not officially support the sending of read receipt requests.

As an alternative, you can use "invisible" email tracking and read receipts, but here you'll have to rely on third-party tracking software. More on that below.

For the other major email platforms, here's how you set them up.

GET SMARTER: 5 clever email tips you’ll wish you knew sooner

 
Outlook
To request a return receipt in Microsoft Outlook, click Options on the top menu bar to bring up its sub-menu.

Check "Request a Read Receipt" to receive a notification when your message is opened.

Additionally, you can also get notifications when your message is successfully delivered by checking "Request a Delivery Receipt."

Mozilla Thunderbird
Click Tools (on the top menu bar) then Options. Now, on the General tab click on "Return Receipts."

Here you can expect Thunderbird to always include return receipts with your emails. You can also send your own return receipts and the location of your receipts. When done, just click OK.

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You can also configure Thunderbird return receipts on individual emails. While writing a new email just click on Options on the top menu bar then select "Return Receipts and or Delivery Status Notification" to configure its return receipt setting.

Again, the recipient can choose whether to send a return receipt reply or not.

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Gmail
In the free version of Gmail, you can’t request a read receipt. But the feature is available via Google's paid option, G Suite.

If you’re a G Suite user, turn on read receipt requests via the G Suite Admin Console. Go to Apps > G Suite > Settings for Gmail > then click Advanced Settings.

Scroll down to the Email Read Receipts section, where you’ll find this wordy option: "Allow email read receipts to be sent to all addresses in my organization as well as the following email addresses." Switch it to “on.”

With this option on, you can click on the lower right down arrow on your Compose window to request a read-receipt for the particular email you're writing.

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Bring in the big guns
Maybe you have a small business. Maybe you're doing research, and you just need to know which emails were opened and which were untouched. In this case, you can try third-party email tracking solutions.

Most of these are paid services with monthly subscriptions, but some have free basic plans, too. These third-party trackers offer more features than your regular free email client.

Just because you want to track those who open your emails doesn’t mean you like the idea of it happening in your inbox. Tap or click here for steps to stop it.

 
GetNotify
One basic way to track your emails and get read receipts is GetNotify. For each message read, you’ll receive a notification. You will be notified of the exact date and time the email was read.

You'll also receive the recipient's IP address, geographical location, operating system and which web browser they are using.

GetNotify's free version caps your tracked emails to a maximum of five per day and a total of 150 a month but you can give a "small donation" to remove the daily limit and increase your monthly limit.

Mailtrack
Mailtrack is a browser extension for Chrome, Firefox, and Opera that's designed to work with Gmail. Mailtrack's free version offers unlimited email tracking, but your emails will be tagged with a Mailtrack Signature. This is typical for individual non-business use.

For about $10 a month, you can get its Pro version to remove the Mailtrack signature. The Pro version also provides tech support, notifications, and usage for three different email addresses.

Streak
Streak is a Customer Relationship Management add-on for Gmail. Their free version has basic CRM features and email power tools. You can track 200 emails a month, which should be plenty for personal use.

Streak also has a Pro Plan ($49/month) and an Enterprise Plan ($129/month) meant for small to large businesses. Aside from full CRM features, these paid plans also include unlimited email tracking.

BONUS TIP FOR EXTRA KNOW-HOW: Tech how-to: Make phone calls from your computer

Roaming and long-distance charges, and using up tons of your minutes, can make phone calls really expensive.

But if you make a phone call through your computer using Wi-Fi, those extra costs vanish. You can even make international calls, and save a ton. Learn how to make calls from your computer, and keep your long-distance loved ones close by.