If you have enabled the user, you can get EV to give it to you.
To identify the Distinguished Name of the mail box you wish to archive. To do this you need to get the ArchiveID of the users archive.
In Admin Console navigate to Archives -> Mailbox, right click on the archive of the user, select properties. In the Advanced tab, highlight the ArchiveID at the bottom, and copy it to the clipboard.
Then back in Admin Console, right click on Archives whilst holding ctrl + shift choose “Find Archives or Folder” and paste the ArchiveID from before into the search bar, then press Find.
In the results pane, there will be a “Legacy Mailbox DN”, this is the Distinguished Name you need for the script.