[X4U] Weird Mail problem

[Michel Treisman]

I have an IMAP connection to a server running Herald. Mail on the  
server is listed in my inbox.  Recently my TiBook stopped seeing mail  
on the server that was sent to me by anyone with the same second  
name, Treisman, as me.  I.e, mail from my kids, or email I send  
myself to test this  out. Any other mail shows up in my inbox, no  
problem.

I threw out com.apple.mail.plist but it made no difference. In the  
end I found the problem seems to be with a document called Envelope  
Index in User/Library/Mail.  I don't know what it does.
If I replace the current Envelope Index in my system with a copy of  
Envelope Index from a backup I made in July, I can see mail from  
Treismans again. That problem is solved, but this creates a new  
problem - my mailboxes, Read, Sent, only show mail up to last July.

Is there any way I can edit Envelope Index (the backup version) so  
that I can see the mail that comes for me from my kids,  and also see  
recent mail stored in my mailboxes?

Mike