OS High Sierra - Run Applescript On Open Email

Yeah true, in fact it might not even apply the rule by rich-click if it is unchecked in Preferences.

Can't you use the AppleScript menu in the System, you can have that icon display on the right side of the menu bar.

I haven't had the AppleScript menu enabled for a while, so I'm not sure what is limiting it.

You could create an Automator Service that gets the email you have selected and runs the AppleScript.

Create a new Automator Service that receives no input in Mail.

Add a Run AppleScript Action from the Utilities menu.

Modify your script (if necessary) to get the selected message(s) and put it into the Action where indicated.

You can delete the "return input" line as the Action doesn't get anything to pass along ("input" argument will be empty).

Save the Service.

Open Keyboard System Preferences, Shortcuts tab.

Find Services in the category list on the left, then find your Service in the list on the right.

Add a shortcut to the Service (cmd-shift-I appears to be open in Mail).

Now, you can select the email message in the list, then type the shortcut to have it run the AppleScript on the selected message.

If the shortcut doesn't work initially, select the Service from the Services menu in the Mail menu. The shortcut should then work (long-standing bug with Services).

You can right-click on individual messages to Apply a rule. Just make sure the tick in preferences next to the rule is turned off, so it won't run on other emails.