Hello,
If you have already deleted your old Mail installation and account, then you may be in trouble. There is a proper method to doing this:
Option 1 will work for Mail to Mail. Option 2 will work for moving mail between any two mail programs.
Option 1:If your new computer does not have any important e-mails that you want to keep. Then you can replace your new system's mail folder with your old system's mail folder.
This is in:
Hard Drive --> Users --> User Name --> Library
In that Library folder, look for the folder called "Mail"
Copy that Mail folder to the same location on the new computer. It will over-write the same folder on the newer computer.
Then, in that same Library folder, look for a folder called "Mail Downloads", if it is present, then copy it to the same location on the new computer.
Then, move in one more level into the folder "Preferences".
This is (from the main hard drive screen) located at:
Hard Drive --> Users --> User Name --> Library --> Preferences
Now, look through the long list of files in that folder, and locate:
com.apple.mail.plist
Copy that file to the same location on the new machine. This will over-write the file with the same name on the new computer.
Now, once you open Mail, it should look like an exact duplicate of what you had on your old computer. Only messages located on your old computer will be on the new system. But, they should all be there. And, all you accounts should be set up as well. So, it should be ready to use.
Since you will be over-writing these folders and files on your new system, it isn't a bad idea to rename the original files on the new system by adding something like .OLD to their name. This way if something goes wrong, you can undo the damage.
All of this can be done using floppy disks, CD-R media, or even transferring files through a network or even a FTP server, or (if you absolutely have to) e-mail.
I have done this to move between OS 10.3.9 and OS 10.4.0 and later.
Now, you must understand that the PLIST file is the key. That's what makes the messages re-appear automatically.
If you still have access to that, then I'd copy that in, and your messages should appear.
Otherwise, if that file is now gone, you could try moving the files from your old e-mail installation into another directory.
Then, go into mail and use the Import feature (under the File menu). Navigate to the mailboxes that you saved from your old e-mail program, and try to import your old messages that way.
If it works, the they will appear in imported folders. But, at least that should get them back. Then you can move the messages where-ever you like.
Now, for option 2:2) If you don't want to use the method above, you can move them through a free trial account of .Mac.
This requires you to set up one of the free 60-day trial .Mac accounts, and configure both computers to work with that account.
Then, you can drag and drop your old e-mail messages from your old Mac's e-mail Inbox (and any other folders you like) into the Inbox on the .Mac account.
Then, simply go to the new machine, and use your e-mail program to check your .Mac account. Then, just drag and drop your messages from the .Mac account's Inbox into your new machine's Inbox.
This method will not cause you to lose messages on the newer machine (unless you make a mistake somewhere).
You can sign-up for .Mac at:
http://www.apple.com/dotmac/Now, if you have not retained your previous Mail installation, and really did only drag the folders from inside Mail, then you may not have anything at all to recover. That would be unfortunate. But, these things do have a method for success. Hopefully, you still have your old Mail installation available to work from.
I Hope this helps.
Let us know if you have other questions.
P.S., if you'd like, go ahead and click the "Helpful" or "Solved" buttons on any of the posts / replies above if you feel they were helpful or adequately answered your question.