Perform a post-incident review instead of a postmortem
I find the name somewhat morbid and ill-chosen because (usually) nobody dies when there are failures in IT systems.
Postmortems may more easily be associated with the need to identify victims and to blame the individuals responsible as well. This distracts from the opportunity to embrace these failures as opportunities to learn and improve.
Instead of performing a postmortem, I prefer to describe this as doing a post-incident review process. This provides neutral terminology and puts emphasis on review of what happened (implying learning) over merely investigating and reporting something.