Export emails in Mac Mail

Step 1: Open the email account in Mac Mail
Step 2: Click on Mailbox and choose Export Mailbox.
Step 3: Choose a folder where the file will be saved or create a new folder, then click Choose button.
Step 4: Mail exports the mailboxes as .mbox file. If you have exported a mailbox already, Mail doesn’t overwrite the existing file; instead, it creates a new .mbox file, such as INBOX2.mbox.