In Mac Mail, how is an archive any different from new mailbox?

The Archive functionality in Mail just creates a mailbox which is disconnected from your service provider.

Most mail accounts these days are IMAP so whether you access them through Mail or a web interface, you see the same mails and can take the same action with them. Archive moves mails out of the IMAP account so they are no longer on the mail server. I don't think there is any more to it than that so calling it archiving is probably a bit of an overstatement.

Hi betaneptune,

We understand you would like to know more about the Archive folder. As noted in the resource below "You can quickly move messages you want to save to the Archive folder to help keep your Inbox from getting too cluttered. Unlike messages you move to the Trash, archived messages remain in your Archive folder until you delete them.":

Archive email in Mail on iCloud.com

Hope this helps!

Have a great day.

betaneptune,

That's a great question. Here is an additional resource from the user guide that goes into more details about Archiving mail that may help:

Archive emails in Mail on Mac

Thank you.