When I restore a cPanel backup into DirectAdmin, DirectAdmin creates the imported cPanel email accounts successfully... but the email_create_post.sh hook script does not run. If I create an email account manually, the hook script runs successfully.
If this is a bug, then it should be brought to the attention of DA developing team. They read the forums regular. So one of the might check it for you.
I'm not sure if it is a bug, or if it is by design. Technically, it is a new email address because DirectAdmin creates the email account from the backup. However, also technically, it is not a new email address in the sense that it is being restored from a backup and therefore the address already existed.
If I had to guess, I'd say the restore process doesn't actually create the email address. It just restores the mail into the appropriate /home/%user%/imap/%domain/%emailuser%/Maildir directory and creates the necessary /etc/virtual/%domain%/passwd - all from the converted cPanel backup.
So there's not really anything that "triggers" a new email account creation.
If this is the case (like I said, I'm just guessing) then the better solution might be to wrap your cPanel to DirectAdmin restores into a custom script, and at the end of the script you can discover all of the email accounts that were created through the restore and apply your email_create_post tasks then.
This is where I kind of part ways with everyone else regarding control panel development. The /usr/local/directadmin/shared/cpanel_to_da/cpanel_to_da.sh script that DirectAdmin provides is a great tool. But instead of DirectAdmin being responsible for every tiny detail - which all would be different for different hosting providers - just provide the script (which they have done) and let individual server administrators wrap their own process around this script.