We have an ICT Service Desk and we have a HR Service Desk.

They need to be able to send emails to one another.  
ICT Service Desk tickets are ##22821##
HR Service Desk tickets are ##HR-9696##

How can updates be automatically assigned to the correct calls, as emails from ICT to HR have the ICT ICT-Ref## number, and emails from HR to ICT have the HR-Ref## number.

Is there a rule that can be put into place.

As you can imagine quite a few emails are sent between the two Service Desk