Hi RichHC,
If you are using the Outlook client, please provide us with the following information:
1. The detailed version of your Outlook client. Check it by navigating to File > Office Account > Office Updates. It looks like 16.0.6965.2115.
2. A screenshot about the blacked area as you mentioned.
3. Does the issue happen on the new emails you created or all the emails in your mailbox?
4. Do any other people around you meet the same issue?
In addition, please try the following steps:
1. Use Outlook Web App with your account and confirm whether the issue occurs. This can help us confirm whether this issue is related to the Outlook client or the account.
2. Open your Outlook client in safe mode. This can disable those Outlook add-ins and help us determine whether the issue is related to add-ins. To open Outlook in safe mode: click on Start > in search, type 'outlook /safe' (Note: there is the space
but not quotation marks in the command)
Regards,
Barry