You did exactly the right thing.

Whenever mail is created (received or written) it is written
immediatelyt to the messages file.  At that point the image can crash,
but the mail safely there.  If you restart your image after the crash,
it will likely not know about the last few messages.

Salvage will find them by looking though the whole messages file.  Those
that it does not have a category for it will put in .unclassified. 
(After salvaging, it probably makes sense to have feedback appear if
.unclassified. now has message, so that people know where to look for
what they thought they had lost.  I will do that shortly along with some
other celeste tweaks).

Mike