You must have a copy of the following files from a computer running High Sierra (10.13) or lower In this example I used files from Sierra (10.12)
If you would like the stationery in the original mail application then skip step 1, disable SIP, and continue with the original application, SIP can be reenabled after. Make copies of everything. Instead of "replace" add a .orig
to the file extension.
Duplicate the Mail Application
Right click on the new Mail Application and go to /Contents/Resources/
Replace the ComposeWindow.toolbar
with the ComposeWindow.toolbar
from the copied files
Go to Finder>Go To Folder>/Library/Application Support/Apple/
Copy the Mail
folder from the copied files to this folder
Open the Mail application and compose a new email
Right Click on the Toolbar and select Customize Toolbar
Drag the icon labeled Show Stationery
to your toolbar and hit done
Click the Show Stationery
button in your toolbar
Note: The toolbar item DOES work with dark mode but the Stationery Panel does not.
macOS Sierra (10.12) Files are available on Github → https://github.com/jbis9051/StationeryMailFiles