There are three message formats to choose from in Outlook: Plain text, HTML, and Rich Text Format. You don't have to designate your favorite format every time you compose a message. Make it your default message format in Outlook instead and apply it automatically to every message.
Outlook 2011 on Mac OS X, v14.1.3, for whatever reason, still does not properly support “format=flowed” content-type or “quoted-printable” extensions for plaintext emails. This causes plaintext emails to be sent as mangled messes, full of arbitrarily inserted linebreaks.
Instructions in this article apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Office 365.
How to Set the Default Message Format in Outlook
Outlook For Mac Plain Text Email Font
HTML is the default message format in Outlook. While plain text format works for all email programs, it doesn’t support text formatting. Rich Text Format (RTF) is only supported by Microsoft Exchange Client versions 4.0 and 5.0 and Outlook.
To configure the default format for new emails in Outlook:
Outlook Plain Text To Html
Go to File > Options.
In the Outlook Options dialog box, select Mail.
Select the Compose messages in this format drop-down arrow and choose the format you want to use as the default for new emails.
Add Outlook Account On Mac
You can set up Outlook to always use plain text or rich text for individual recipients regardless of the default message format you specify.