In Microsoft Outlook 2016 for Mac, and in Outlook for Mac 2011 version 14.2.4 and later versions, you can select the default text encoding that is used to compose new messages.
To access the composing preferences in Outlook 2016 for Mac and Outlook for Mac 2011 14.2.4 and later versions, follow these steps:
From the main toolbar, select Outlook.
Select Preferences, and then select Composing.
Click to select the Preferred encoding for new messages check box.
Select your encoding preference from the dropdown menu.
The encoding that you select in the composing preferences will be applied to all new messages.
This preference was created because, under certain circumstances, the automatic encoding that Outlook for Mac performs may result in unexpected characters in messages that are sent. This preference enables you to select an alternative text encoding (such as Unicode) that will be applied to all outgoing messages. In earlier versions of Outlook for Mac, a change of text encoding could only be performed for individual messages.
Outlook 2016 for Mac, Outlook for Mac 2011, version 14.2.4, default text encoding