If any users had been added to the system with the old domain ("hotmail.com"), their email addresses would have automatically been changed to contain the new, fake (and archived) domain (hotmail-123.com). So
jsmith@hotmail.com
would now be
jsmith@hotmail-123.com
. Find each of those users (searching by the new, fake domain) and move them to the correct organisation, and at the same time change their email domain back to the correct domain ("ibm.com"), by using the instructions found
here.