How can I read mail that is on my hard drive?

Question

Whew, this is so tough that I can't even really describe what is happening.
Yet my hunch is that the solution is very easy if you know how to use a computer. (I've been using Macs/PCs for decades but am apparently clueless about certain aspects.)
I use Mac Mail in OS 10.4.
I notice that in my Admin/Library/Mail that all my mail is in various folders.
(There is no Mail folder in my name account, only in Admin. My impression is that I am the Admin and that I don't often use my name account, but I don't really know how that all works.)
I back up those folders to a remote drive.
I would look to look at some of that email again.
The email I would like to look at is in the Sent Messages.mbox folder within the POP-[my email address] folder within the Mail folder.
If I backup then delete the current "Sent Messages.mbox" folder and replace it with the folder of the same name that has old email in it that I want to look at, I have no luck.
The program keeps pointing to the current Sent mail even though it's trashed.
So that part of the program must be looking at mail that is not on my hard drive but which is on a remote email server.
How can I make Mac Mail look at a folder on the hard drive instead of on the server?
I have a vague understanding of the mail "On My Mac" vs. mail on the server, but I don't know how to control what the program is looking at. I wish I could just have it "Open" a folder that I pointed to.
I've been searching and googling about the subject for hours with no luck. I'll will keep trying.
(I previously had a question here on a related subject. I backed up the old mail and deleted unwanted mail and it still seemed to be in the Mac program. Some folks tried to help me but they suggested that I do things which were very difficult to me, just as download and compare files using a 3rd party program that is something like Spotlight to look at hidden files, I guess, but which doesn't work with 10.4. I forget the name of it. I think I must be missing something really obvious about mail stored on a hard drive versus mail stored on a server, but which is also opaquely handled on the Mac -- that is, a nonexpert might easily mishandle it. But I recently tried taking some of their advice and got nowhere and I see that the question is archived now.)
Help?
Thanks. -- JP

Answer 1

No, I don't think so. I think I gave all the specifics that I can imagine in my first post. I had email that I received and replied to in my SENT folder. I believe it came in from my POP server and went out that way, too. I backed it up on a remote drive. So there was a SENT folder on that remote drive. Now I'm trying to look at it again. Via the Mail program. I've copied that old SENT folder into my Library>Mail>POP folder where it came from. But I am only able to look at recent/new SENT mail. I want the Mail program to point to that old folder of SENT mail. I'm the only person who uses this computer. All my mail seems to end up in my Admin folder. I do have a Username folder but no mail goes there. It doesn't seem to be the folder/acc't that I use, but who knows. I just type on the computer and use it. I didn't set it up. A friend gave it to me years ago.