i think youre mistaken. i have been using mail exclusively for years now and have never once seen the behaviour you describe.
I to have been using it for year and never had this problem before... Type in the search and no matter what folder the email was in it would come up... I think i could even type something from the body and it would still come up... Not sure why its not working something has definitely change
I never had the problem with Mail searches that you describe and I have been using Apple Mail and that search for years.
Possible that something in the Mail application became corrupt.
To answer your original question - as far as I know there is nothing other than the search options across the top of the Mail window to customize the searches.
Maybe shut down and restart Mail....or if that doesn't change anything, even consider re-installing Mail.
What version of Mail are you on?
I don't know if you're using Apple Mail with any POP or IMAP accounts and your 'search' problem shouldn't matter, but you could try setting up a new 'testuser' account, and setup the same accounts you're using and having the problem with (and make sure to leave any messages on the server) and do some 'search' tests and see if they work.
My experience has been that any Apple Mail problems are usually to do with the actual user's Mail settings and accounts preferences etc. rather than the actual Mail application - just to save Trashing and re-installing the Mail application. But be aware of any non-Apple third party software that might be part of your Mail 'search' problem.
If your Mail account settings and stuff work when logged in and using the 'testuser' account then you'll know that the Mail application isn't the cause of the problem.
But a proper Trash and a clean re-install of the application and any possible updates doesn't take too long to do.
doesn't really seem likely that an application, especially one that's part of the original install became corrupt so i'm with pm-r that i'd try other things first... a simple restart of the os often can 'fix' weird behaviours, and removing the plist files is also an option... a run of maintenance or onyx is also not out of the question... and then there's the internal mail helpers like the rebuild mailboxes command.
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