Generally, there are three ways with the Mail app in OS X that Mac users can use in order to control the flow of emails in their inbox. These include:
When compared to 1st and 2nd methods, 3rd option was found a better way is to use Apple. To utilize the Mail’s Export Mailbox feature, users need to create mailboxes for groups of messages to export their mailboxes, making an .mbox file on their computer. Apple Mail Support
Create a mailbox by opening Mail and going to Mailbox > New Mailbox. This command will get mailboxes in the left sidebar of the Mail window. Here, you can drag and drop messages to the mailboxes as it will help you remove messages from the Inbox. To export a Mailbox, Mac users need to go for the following instructions:
After exporting a mailbox, you need to get rid of the mailbox’s messages. The same thing can be made possible by deleting the mailbox. You can also move all of Mailbox messages to Mail’s trash or, if you prefer to retain the mailbox but not its messages. Mac Outlook Support
When it comes to import Mailboxes, you may need to look at earlier exported messages. There, you can import messages back to Mail. Another email app .mbox format can also be used for the same purpose.
For importing back into Mail:
Remember: Mail creates an Import folder in the On My Mac section at its sidebar for each imported mailbox.