To change the message margins in Outlook 2013 please follow these steps.

Step 1. Create a new email message

Open up outlook and click on New Email

Step 2. Click in the body of the email

Step 3. Click on Paragraph Settings

Click on the “Format Text” tab up the top and then click on the little expander icon under the section “Paragraph”

Step 4. Change the Paragraph Settings

Change the Margins by adjusting the Indentation Settings as in the image below.

Step 5. Set as Default

Click on the “Set As Default” button down the bottom of the dialogue box

Conclusion

Changing the Margin settings in Outlook 2013 for composing emails has limited options but doable.  Just be aware that whatever settings you put in here may be either ignored by the email client on the other end or may cause readability issues depending on the size of the screen they are using so use cautiously.