Mail's Search function looks pretty simple. Choose
either the current mailbox or "All" boxes. Then decide if you want to search in
one these To:, From:, Subject: or the entire body. Not much choice, right?
Well, how about this, from "joekewe" in a Macworld <
comment (#6)>:
QUOTE
More complex searches are easily accomplished in Mail.app for free. Choose "Entire Message" then you can enter: [search string] [from:sender] [to:recipient] [subject:subject] in the regular Mail search box. Probably enough for most needs without switching apps. Note that the [brackets] represent optional criteria. Do NOT type the brackets, and don't forget to choose "Entire Message" or it won't work. You can select "this" mailbox or "All Mailboxes" to search as usual. No need to spend $30 and switch applications for this functionality.
This is similar to how it can be done in Spotlight, which is probably the core function used in Mail, of course.