Cyrus IMAP Mailbox Recovery

I’ve occasionally encountered IMAP mailboxes that were unreadable and undeletable
using any mail client. In Mac OS X Mail, this usually produces an “Unable to Select” error.

Here’s how to fix the server-side mailbox. At the bottom is a bonus: how to recover the locally cached .imapmbox file from Mail.

I learned how to do these steps from two web pages: Bynari Support and Code Comments.

Step 1: Backup the locally-cached mail

The file will be inside ~/Library/Mail/IMAP-email-address, with an extension “.imapmbox”. Copy this file to your Desktop.

Step 2: Repairing the Cyrus folder

1. Use Server Admin to stop the mail server
2. Change to root, and enter the directory /var/imap:

   # sudo -s
   # cd /var/imap

3. backup mailboxes.db:

   # cp mailboxes.db mailboxes.db-backup

4. Using Workgroup Manager, set user cyrus’s shell to bash

(Ed. note: Rather than give cyrus a shell you could just use sudo -u cyrus to do the following steps.)

5. su to cyrus, and dump the database to a text file:

   # su cyrus
   # /usr/bin/cyrus/bin/ctl_mboxlist -d > /tmp/mboxlist.txt

6. Edit the text file and remove the lines that contain the problem folders:

   # pico /tmp/mboxlist.txt
   

7. remove mailboxes.db:

   # rm mailboxes.db

8. rebuild mailboxes.db from the new text file:

   # cat /tmp/mboxlist.txt | /usr/bin/cyrus/bin/ctl_mboxlist -u

9. Reconstruct all mailboxes

   # /usr/bin/cyrus/bin/reconstruct -r -f user

   If there are any remaining folders that print an error, they’ll be listed when performing cyrus reconstruct: (ie.. user.someuser: Mailbox does not exist).

10. Exit back from cyrus and root

    # exit
    # exit

11. Using Workgroup Manager, set user cyrus’s shell back to /usr/bin/false.
12. Restart Mail using Server Admin

Step Three: Recovering a locally-cached imapmbox

1. Create a fake imap email account. Don’t use a real name or password. We want the account to remain offline.
2. Quit Mail

3. In the Finder, open the directory holding the newly-created INBOX.imapmbox file (It’s in ~/Library/Mail/IMAP-something/”).

4. Move this (empty) INBOX.imapmbox to the trash.

5. Move the cached mail file you had copied to the Desktop to this folder. Rename the file to “INBOX.imapmbox”.

6. Start Mail again, and click on the new account name. Your messages should reappear.

7. Copy the messages from this folder to another one, either IMAP or locally.

8. In Mail’s preferences, delete the account you had created.

Make sure you keep this fake account offline, or else Mail will overwrite your cached mailbox with an empty one!