Importing Archive in Mail.app is not working for many people, the solution is not clear of the Web Search.. the Following is the workaround.
Fixes issues of bug in Import: the problem importing mbox or Apple files that contain other mbox files (mailboxes inside mailboxes or think of it as folders inside folders) does not work.
- Move the lowest possible mailbox/folder to a tmp folder on your desktop.
- go to Import Mailbox in Mail.app and now select all the mbox files in the tmp folder you want to import.. example “2014 April Inbox.mbox” to “2014 October Inbox.mbox”
- Follow the instruction / gui to comple the import in mail.app
- move the mbox file to the original folder (Note: I use Move instead of copy.. copy take a long time when the file size is large)
You will now have your mails imported into “import folder” on My Mac. and the folder is saved in Macintosh HD ▸ Users ▸ XXX ▸ Library ▸ Mail ▸ V2 ▸ Mailboxes.
Hope this solve problem of many..