[Evolution] Recurring Problem with Sent Mail Folder

[Barbara Tobias <barbtobias09 gmail com>]

I am using Evolution 2.28.1 and Ubuntu 9.4.  Some weeks ago, my sent
folder became corrupted.  Thanks to some help from this list, I was able
to delete the folder and have it start accumulating outgoing mail again.
However, yesterday I noticed that it had happened again.  

Does anyone know what might be causing this?  I now know how to fix it,
but still lose some history of what I've done, and I'd like to avoid
that if possible.

Thanks.

        Barbara Tobias