First of all, before you try to delete the mail in question, open your
control panel and choose classic view. Then open Folder Option and click on
View. Then, under hidden files and folders, make sure you have 'show hidden
files and folders' checked.
1. Back up the email you wish to keep. While rebuilding the mailstore
shouldn't result in any loss of email, it is always better to be safe.
2. Close Windows Mail.
3. Click the Start Button and select Computer.
4. Navigate to C:\Users\your username/AppData/Local/Microsoft/WindowsMail.
5. Delete WindowsMail.MSMessageStore.
6. Open the Backup directory.
7. Open the new directory.
8. Delete WindowsMail.MSMessageStore.
9. Open Windows Mail to rebuild the mailstore database.
You should now be able to view and delete the problematic message(s).
What I would then suggest is you reverse the Folder Options I mentioned at
the start. Put it b\ck as it was by NOT showing hidden files and folders.
Although this is not 100% necessary.