mail quits with "cannot save information

This happens every session of mac mail usually after using mail a few minutes but sometimes right away with no chance to read or change anything.

The message says to quit mail and delete (something) but how does one delete with out being in mail and frelling the mail database in the process?

This shows the V9 folder under mail and 2 sub folders that all 3 show 2 differing numbers of size used in the folders (V9 pretty much sums the sizes of 9f... & 6B... plus E8...) ?? What does that mean and how to safely change the dicotomy?

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[Edited by Moderator]