//Log in to the program using your previous username and password. Most computer-based email Programs like Outlook and Thunderbird automatically transfer your entire account to a new computer, as long as your Internet Service Provider(ISP) is made aware that you are transferring messages and changed your settings to enable your information to appear on more than one computer. If logging in with your email address and password does not import your messages, contact your ISP.
Click on "Options" inside your email program and choose "Import." You can choose to import files, addresses, contacts, messages, and folders. Click "Ok " to import these items. You will need to enter your email address and the password you used on your old computer to complete the import process//
https://www.techwalla.com/articles/how-to-transfer-email-to-a-new-computer