That removes the messages from the mail server, leaving it stored only on your Mac.

On the behavior side, create all the mailboxes you need under the On My Mac section of the Mailboxes list, and then as you receive email in your Inbox, file those locally into those folders. Appears to be some sort of sync issue but it is using a lot of memory and causing the computer to run slower. It often displays that several 1000 messages are being downloaded. An odd issue has arisen wherein my Mac Mail is constantly displays a 'Downloading Messages' message when no new emails are being downloaded. Now all the standard Mail behavior will result in messages being downloaded or stored on your Mac. Mac Mail Constantly 'Downloading Messages'. (If no mailbox exists, you need to create it from the Mailboxes sidebar. In the Mailbox Behaviors tab, for each mailbox popup menu, select a mailbox listed under On My Mac.(The only reason to avoid this if you get frequent large attachments in messages you delete without needing those attachments.) In the Account Information tab, set Download Attachments to All.Select Mail > Preferences and click Accounts.You make one change in settings and one change in behavior for everything else. The Inbox is essentially a window into messages that have arrived and you haven’t processed. Your Inbox will always remain on the server.

Apple mail download more than 60 days