There may be an issues with mail when updating to Tiger (10.4) where
your mail will not import old emails properly or at all. It seems
people have been experiencing a variety of problems related to this.
For more information you can go to this site
http://forums.macnn.com/showthread.php?t=253160
however I'd advise you to refrain from taking the solutions on that
site as gospel. You certainly should not rename your mail folder
before upgrading. Instead make sure you back up your mail folder
(found in ~users/library) along with anything else important.
I experienced a problem with importing old emails from the mail
program after performing a clean install. I attempted to use the
mail program to import old mails by directing it to my backed up
folder. It wouldn't import anything that way.
Now this is the useful part... I fixed the problem by quitting mail
then moving the mail folder (in the ~users/library folder) to the
hard drive and replacing it with a copy of my backed up mail folder.
I then ran the mail program and it imported all of my old emails.
They were all marked as unread but that's a problem easy fixed.
Perhaps this will be useful to someone else
Ruben A. Franke