Question: How do we delete apple.com.Mail.Backup
Has anyone tried the last post in this thread?
I'm afraid to be the first!!!
(Here is the post from above link)
Go to your User's Library folder**
Scroll down to Mail
In the V4 folder you should see something similar to this:
(Note: each account will have it's own folder and the "On My Mac" folders will also have it's own folder. This example is for one account and the "On My Mac" folders)
Look in the alphanumeric folders to locate your "On My Mac" folders. the Outbox is in in the local folders. You should see the com.apple.Mail.Backup folder.
Delete this folder.
Next in MailData folder, delete the three files with envelope in the name.
Log out under the Apple in the Menu bar.
Log in and empty the trash.
Open Mail. Mail will reindex your data.
When indexing is complete, Mail will open
** Show User's Library
The User's Library folder is hidden by default. To unhide: Select the Finder in the Dock. Under Go in the Menu bar > hold down the Option key and you’ll see the Library.
Finding the User Library Folder
iMac, macOS High Sierra (10.13.3)