How to transfer only one email account to a new iMac

[Onamuji]

bedouin wrote:
Now I just want one old email account. Can I just do a export? Will that take all my sent and received emails on that one pop account?

Export each mailbox/folder that you want to keep to mbox. Can be done with a right-click (control-click) on the mailbox/folder in the list on the left side of your Mail window.

Use Mail's import command on each mbox folder that you copy to the other Mac. It'll come in as "on my Mac" mailboxes/folders.