Useful for form letters and other emails when you need to use chunks of the same text.
This information is from these two Microsoft articles:
On the Home menu, click New E-mail. Keyboard shortcut To create an email message, press CTRL+SHIFT+M.
In the message body, enter the content that you want.
In the message window, click File > Save As.
In the Save As dialog box, in the Save as type list, click Outlook Template.
In the File name box, type a name for your template, and then click Save.
By default templates are saved in the following location:
c:\users\username\appdata\roaming\microsoft\templates
Select New Items > More Items > Choose Form.
In the Choose Form dialog box, in Look In, click User Templates in File System.
The default templates folder is opened. The folder location (in Windows 7 and later operating systems) is c:\users\username\appdata\roaming\microsoft\templates. If your template is saved in a different folder, click Browse, and then select the template.
Select the template, and then click Open.
Make any additions or revisions to the recipients in the To, Cc, or Bcc boxes and any changes to the subject and message body.
Note: Changes made aren’t saved to the template. If you use the Save command, this creates a draft of your message, but won’t update the template. To update the template, follow the steps for saving a new template.
Click Send.