You have a couple methods - for one thing the user's email is stored in Dovecot under a folder with their UUID. If you remove the user and recreate the user with the same user ID and GUID (have to do this bit using the Inspector feature) you can avoid having to migrate the data to the new GUID/user ID. This will often times fix issues with a user that are caused by the Directory.
The easiest method to back up his/her email is to copy their folder (default location is: /var/spool/imap/dovecot/mail/GUID
) using ditto
. You can determine the user's GUID by either looking in Workgroup Manager or using dscl
(eg. Local User:dscl . read /Users/shortusername | grep GeneratedUID
or for a OD user dscl /LDAPv3/IP_OF_OD_SERVER read /Users/shortusername | grep GeneratuedUID
). You can find more about Apple's recommended method for backing up on Page 81 of their documentation; Mail Service Administration