Outlook uses Word as the HTML rendering engine and although many features have been added over the years and marketers have compensated for these limitations, it could still sometimes end up in a malformed display of the email message.
In short; The Word HTML rendering engine doesn’t provide support for things like animated gifs (unless you are using Outlook as part of a Microsoft 365 subscription), advanced css formatting and HTML forms, accessibility and more.
To overcome this, there is the “View in Browser” command in Outlook but that still opens the message in the ancient Internet Explorer.
This guide explains how you can render the message in a browser of your choice like Microsoft Edge, Google Chrome or Firefox by a click of a button.
An additional benefit of opening the message in an Internet browser is that you have the printing options of the browser available to you and therefore also the option to only print your selection.