Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi Sam,
I suggest you open Outlook, click on File> Options> Language> under Choose Editing Languages check if any other language is enabled, if yes highlight it and click on Remove.
Based on your description, this issue should be related to your client side rather than server side. Please try HTML format message to see if the same issue occurs.
Additionally, there is a similar thread for your reference: Outlook email text become weird characters.
If the suggestion above doesn’t help, please let us know the following information:
- The whole screenshots reproducing this issue.
- Your Outlook client version details such as 1704(8067.2020).
- Have you ever done anything when this issue happened?
- Are these senders and group who encounter this issue in pure cloud or sync from on-premises? In other words, when this issue occurs, are these mailboxes in pure cloud or on-premises?
With the information above, we can move forward.
Best Regards,
Vanessa