How to delete Mail account without losing old mail?

Question

I've recently changed ISPs, so I have three old accounts/addresses in Mail that are no use any more. I want to delete them, but Mail (and Mail Help) tells me if I do I'll lose all the mail that has been sent or received from/by those accounts. I tried unchecking the Enable box in the Advanced tab in Preferences:Accounts, but then all the mail the disabled address had received (hundreds of messages) disappeared. I was able to get them back by re-enabling the address, but now I again have three extra addresses in the selection popup on new messages, so if I don't catch it, a message can be "sent" by a non-existent address. (It bounces, and I have to select the right address and send it again.) I don't want to lose years of emails, I just want to delete some addresses I no longer use. Anyone know how?
PowerBook G4 17" 1.5GHz   Mac OS X (10.4.3)  

Answer 1

Open "In" in the mailboxes drawer by selecting the black triangle beside it....
Thanks for the further elucidation. Wish I'd known all this (which is not explained anywhere in Mail's online Help, at least not that I could find) before I went through the tedium of manually sorting through all the messages. And I still don't understand why a search of the Inbox by the to-be-deleted email addresses failed to find some 20 messages which appeared in those addresses' individual boxes when I expanded the Inbox to show individual accounts.
Many other email clients utilize a single large database file which is not dependent on individual account and associated mailbox filing. ... Entourage uses a single large database file and I don't prefer using an email client that stores all data in a single file.
I certainly agree, and in fact was horrified to learn that Outlook Express does the same, which has resulted in disasters for many users. "All your eggs in one basket," anyone? Funny how folks are always pointing out to me that Apple software, despite glaring flaws, is better than Micro$oft. Since I got my first Mac in 1988, I've never used any Micro$oftware -- or any other computer. "Better than Microsoft" is not the same as "as good as it could be with a little effort," and nowhere near the "insanely great" of the early Macintosh years.
In the early Internet years I used Netscape, which was excellent in its time; in the last few Classic Mac years, when Netscape 4.x simply couldn't do the job anymore (and Netscape 6 turned out a disaster), I switched to iCab and Eudora. I stayed with Eudora in X 10.2, finally switching to Mail sometime in 10.3, because Eudora was, well, looking increasingly ugly in the X environment, and Mail is part of the OS X package and Unicode-savvy (one of OS X's primary draws for me), and I figured I'd better become familiar with it since I support other Mac users.
In Eudora, which does not store all mail in a single database (each mailbox is a single file, not encrypted, easily readable in a text editor), and which BTW comes with a comprehensive PDF manual, "When you delete a personality, all messages associated with that personality (both incoming and outgoing) are assigned to your Dominant personality." Which doesn't require the user to do a lot of research and work to avoid losing years of mail, and makes a lot more sense to me. And is why it had never occurred to me before that such a simple thing could turn into such a hassle; I've changed addresses before and never noticed a hole in the road. So it can be done. Eudora also keeps its mail in the Documents folder, a lot easier to back up than Mail's, which the user must hunt for.
And yes, I've been tempted to return to Eudora -- I never see any online posts about "Eudora just lost all my mail!!!" while I see many such about Mail -- but it would be a big hassle (Mail's proprietary mbox files are not easily readable by anyone else), and like I said, I have to be familiar with Apple's software, since it's what my clients will be using. I certainly do prefer Mail's look & feel, if not some of its quirks.
I did some research to find out more about the filing structure for each email client....
Nice if you have the time/energy and knowledge/expertise to do that kind of research, but most users don't, and prefer the software to "just work" in a way a non-techie user (who paid as much -- or more -- for the computer as the software engineering major) would intuitively expect. As in not tossing all your mail just because you've changed your address.
There is one more thing you can do which is mark your question as answered.
Thanks again for taking the time to explain all this, and I'll mark the question "answered" now. And get back to work.
PowerBook G4 17" 1.5GHz   Mac OS X (10.4.3)