MAIL WON'T STOP INDEXING

G4 iBook OSX 10.3.9, Mail 1.3.3

As user A on this Mac I sent a brief Mail email with about 46 MB of photo attachments to several users including myself.
Today that message appeared in the IN folders of all the addressees, as expected.
BUT the Mail Activity Viewer on the iBook keeps showing message
"Indexing 23 of 30:"then shows the email Subject/title"
And this persists after all the actions I can think of, including the following:

RESTART, Moving that message from IN and SENT folders to Trash folder, Emptying Trash, Using "Delete" button on Mail window, Erasing all the deleted messages for that sender user.
Clicking on the red STOP button in Activity Viewer only results in a "STOPPING' message appearing.
Another "Indexing" message starts again later.
Now states "Indexing 0 of 3:then shows the email Subject/title"

There is no problem on the computers of the recipients of the email.

Short of throwing the thing in the bin, is there some other way of bringing INDEXING to a halt?

Try to select the inbox then menu>mailbox>rebuild

In reply to a post by stniuk:

Try to select the inbox then menu>mailbox>rebuild

Thanks - I have tried that for all the folders which seem relevant.
The 'problem' email is in a named Folder, not in the IN folder.

After rebuilding several Folders.including IN, the Activity Viewer still shows Mail attempting to index the thing.

After moving all the messages from the problem folder into several new folders, in an attempt to locate the trouble. the mad indexing is still being attempted.

I could try to ignore it, I suppose, but that might just be storing up trouble for later.

Apple Discussions includes:

https://discussions.apple.com/message/2469516?search...

but that is directed at problems with IN folder, so I have not yet tried that approach.