Out of the box, macOS Mail doesn’t support read receipts—notifications that the recipient of your email has opened it. However, you can use Terminal to make the necessary changes, allowing you to confirm that an email has been delivered to your recipient’s inbox. Here’s how to do it on a Mac running OS X 10.8 (Mountain Lion) or later.

You can enable this feature as follows:

Open Terminal, found under ~/Applications/Utilities/.

At the prompt, type the following command and press Return: