I have microsoft 365 and the last update has made the message area FONT extrememly tiny. How do it get that changed back ?

Reset the Outlook message editor’s zoom first: click inside the message body, hold Ctrl, and scroll the mouse wheel up until the text is readable again.

This is the closest match when the text suddenly appears tiny while typing, particularly if Outlook’s font-size box still shows a normal value. You can also try Ctrl + Plus (+) in the message body.^1^

If every new message still uses a tiny font

The permanent setting depends on which Outlook desktop version you use.

New Outlook for Windows

1. Select View → View settings.
2. Select Mail → Compose.
3. Under Message format, choose the desired font and size.
4. Select Save.

Classic Outlook

1. Select File → Options → Mail.
2. Under Compose messages, select Stationery and Fonts.
3. On Personal Stationery, select Font under:
   • New mail messages
   • Replying or forwarding messages
4. Choose a readable size, then select OK three times.

New messages and replies/forwards have independent settings, so adjust both sections. To restore classic Outlook’s initial settings, select +Body, Regular, 11, and Automatic color.^2^

Create a new message afterward and type a few words. If the font-size box shows the chosen size but the text is still visually tiny, adjust the editor zoom again rather than increasing the actual message font.

If received messages are also tiny

• Classic Outlook: In the Reading Pane, move the zoom slider at the lower-right to the right. Select the percentage beside it, choose a zoom level, enable Remember my preference, and select OK.
• New Outlook: Open a message, then select View → Zoom → +.^2^

References

1. Font Size is too small - Microsoft Q&A
2. Change the default font or text color for email messages in Outlook | Microsoft Support