Solve: Mac Mail Not Working

Many Mac users complain that after updating their system to Mac OS Mojave, the Mail app just quits and crashes. To resolve the issue, you can try the following instructions. These instructions will be useful for any Mac OS version:

First, try and run your Applications folder instead of doing it from the dock.
In your Finder, open the Applications folder. Click the Mac Mail app to open it.
If you are able to perform the above steps, you can try to remove the Mail icon from the dock and then add it again.
When your Mail app is open, its icon will display on the right-hand side of your dock.
Now, you just have to click the Mail icon and drag it to the left. It will remain there in the dock.
If the above steps fail to resolve the issue, try restarting your Mac. To do the same, make use of the following steps:
In the upper-left corner of your screen, click the Apple logo. From the menu that displays next, you can see the Restart option.
Click Restart and then you will see a pop-up. Here, click the Restart button. Your Mac will now reboot.
Once the rebooting is completed, check whether your Mail app is opening.

In some situations, the Mac Mail app will freeze and become unresponsive. If this is the situation, you can try force-quitting the app. To do the same, follow the steps given below:
In your dock, right-click the Mail app icon and from the pop-up that appears, choose the option that will force-quit the app.
If force-quitting does not work, you can try terminating the Mail app in your Activity Monitor.
After you terminate the app using the Activity Monitor, try to reopen the Mac Mail app.