Hi Floyd,
Generally, rules fall into one of two categories—organization or notification. A rule runs automatically on incoming or outgoing messages. See
this article about how to manage email messages by using rules. So I am afraid it is not possible to realize your requirement by rules.
In this situation, you may consider the following workarounds and see if it can be helpful:
Workaround 1: Add frequently used templates to Outlook’s Jump List
1. Simply drag & drop a saved template file (oft, msg or eml file) onto the Outlook icon in the Taskbar:
2. When you now right click on the Outlook icon in the taskbar, you'll see the pinned items:

Workaround 2: Use a Quick Step
Apart from using templates, an alternative is that we can create a Quick Step instead.
1. Go to Hone > Quick Steps group, choose the Create New option.
2. Enter a name for the new Quick Step.
3. From the Choose An Action drop-down, select New Message, click Show Options.
4. Enter the template text:

5. From the Shortcut Key drop-down, select a predefined shortcut if necessary, click Finish. It will now appear in the Quick Step section. Click the quick step item name to use the template.
Hope the above information can be helpful.
Best regards,
Yuki Sun
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