Quick Parts in Outlook are the equivalent of AutoText in Microsoft Word.
In the message text pane, type the text that you want to use as a Quick Part.
Apply any required formatting to the text.
Select the text so as to highlight it.
From the Insert tab, Text group, click on Quick Parts.
In the Create New Building Block dialog box, enter a short name for the quick part in the Name box.
If desired, type a longer description of the quick part in the Description box.
Click on the icon at the end of the row of icons in the Quick Access Toolbar.
Click on More commands... in the drop-down menu.
In the Choose Commands from box, select All Commands.
In the list of commands, scroll down then click on Quick Parts (commands are in alphabetical order) then click on Add >> (see the illustration below).
In the message text pane of the email you're composing, enter the short name for your Quick Part as entered in step 7 of the Creating a Quick Part instructions above.
Press the F3 key and the text of the selected Quick Part will appear in the message text pane.
While in the text window of the email you're composing, click the Insert tab.
Click on the Text button in the ribbon and then click on Quick Parts, then click on the quick part you want to insert into your message.
Click on the Quick Parts icon in the Quick Access Toolbar.
Click on the Quick Part item you want to insert into your message. Its text should then appear in your message text window.
Start with a new email, and click in the message text pane.
Insert the required Quick Part into the message text as described in the Inserting a Quick Part... section above.
Modify the inserted text as required.
From the Insert tab, in the Text group, click on Quick Parts.
The Create New Building Block dialog box will be displayed.
In the Name box, enter the short name for your Quick Part as entered in step 7 of the Creating a Quick Part instructions. Then click OK.
Click on Yes when you are asked Do you want to redefine the building block entry?
Click on New as if to compose a new email, and click in the message text pane.
A gallery of your Quick Parts will be shown.
Close the New Message window to cancel the message.
NOTE: Outlook Quick Parts, like Word Autotext items, are stored in a file called NormalEmail.dotm (in ..\AppData\Roaming\Microsoft\Templates).