You will learn here how to do something that no-one anywhere else on the internet can do!
The problem: for some bizarre reason, when you delete a mailbox in Apple’s Mail, instead of going to the Trash in Mail or the Trash in the computer, the folder and files just disappear. The dialogue box says (in one sense correctly) ‘This action cannot be undone’. However, it can because the files are still on your drive.
So you need to:
1. Search for them using Spotlight. This will not allow you to recover them by original folder, but if you have, for example, deleted all the messages from Uncle Albert by deleting your ‘Uncle Albert’ mailbox, then a search for his name will bring them all up. Because they are hidden, you cannot see the ‘crumb trail’ location.
2. Click ‘Show all’ in Spotlight, then sort by type of file, so all the Mail messages are together.
3. Create a new folder on your desktop and name it eg ‘Uncle Albert’. Drag all the Mail messages from the Spotlight window into this folder and voila you have recovered the messages.
4. However, this is only half the job, as they are not back in Mail. And Mail will not allow you to import individual messages (which are in emlx format), only whole mailboxes. So you need to download the ’emlx to mailbox converter’ which you can find here. If you are nice, you will give the man a donation for saving you $79.95 and a lot of hassle buying and using data recovery software.
5. Open ‘Uncle Albert’ (the folder, that is) and launch ’emxl to mbox converter’. Highlight and drag all the Mail messages into the window, and click Save mbox… adding a name, such as Uncle Albert.
6. Go to Mail, and click File/Import Mailboxes… follow the instructions and import Uncle Albert.mbox.
Now, this is not perfect, since you are not strictly recovering the deleted mailbox, so you will have to do some sorting. But, heh, that will teach you not to delete it again. But I have found no other way anywhere on the www to do this. I hope you are grateful!!
And I must credit my good friend James Blandford-Baker for invaluable technical and moral support in going through this process myself.