such messages would be marked expunged in the database, then the junkfilter
would be retrained for the removal of the message. but during retraining, the
expunged flag would be cleared again. the on-disk message file would still be
removed. so when opening the mailbox, the message would appear to still exist,
but cannot be retrieved from disk.
if you run "mox fixmsgsize", and you get warnings about missing message files,
you could create empty files (with "touch"), run "mox fixsmsgsize" again,
followed by "mox recalculatemailboxcounts <affectedaccount>" and run "mox
bumpuidvalidity <affectaccount>".
"mox backup" would probably also complain, as would "mox verifydata".
this may have caused the "wrong mailbox counts" error i got from "mox
verifydata" on a backup.