Hi Terry,
Based on my assumption, do you mean there is nothing in Outbox, but Outlook continues to show "Sending message" at the lower right of the window?
If this is the case, this could be caused by a stuck read receipt. As read receipts are invisible in your Outbox, you may use the MFCMAPI tool to delete them:
- Download and run the latest version of MFCMAPI via MFCMAPI page on GitHub. (Use MFCMAPI.exe for 32-bit version of Outlook, and MFCMAPI.exe.x64
if you are using a 64-bit version of Outlook.)
- Press OK on the first screen and then click Session > Logon.
-
Select your Outlook mail profile.

-
Double click on the line which has the value for the Default Store column set to True.

-
Right click on Root-Mailbox (or Root Container)in the left panel and choose: Open contents table.

-
Check if there is any item whose subject is prefixed with the “Read, delete the item and restart Outlook to check it the issue can be fixed:
Hope this can be helpful.
Regards,
Yuki Sun
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