A Microsoft Outlook update released today for the desktop client introduced bugs that prevent users from creating or viewing mail. Users of the click-to-run desktop client found that they could no longer properly view emails or create new ones. Instead of seeing an entire email, instead of seeing the entire message body, they only see a small portion or a single line of the email message. When creating a new email message, every time you press enter, all the previously written content will be removed. Users with access to other protocols, such as Outlook on the web or the Outlook mobile app, can view message content.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-outlook-bug-prevents-viewing-or-creating-email-worldwide/