Under Email Encryption you describe some Programs for use with NK’s. For Mac User that would like to use the MacOS build in Mail, there is another Toolsuite MacGPG available. The advantage is a build-in mail plug-in with some graphical tools for Setup and Key Administration (GPG KeyChain).
The disadvantage is, that you need to pay for a support plan ( around $25 ) in case you want to use the plug-in.
… Just in case you want to Update your documentation for macOS (the not so new name of Mac OSX) 
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I thought using gpg-tools does work with Mail right away?
Yes, but only temporary. They changed the support model. It was free until the last or the release before. You could still install it today without a plan, after the test phase ( around 30 days when I remember) the mail plugin doesn’t work any longer ( and makes trouble if you keep it ). You coudl also install the Tools without the Mail Plugin to get the UI for Mac (without the Mail )