Hi Brad043,
I reached out to one of our product specialists, and they said they may be able to provide a more detailed answer if we knew the messaging system you are using? I was still able to get this however;
"While on-prem email systems and hosted email systems appear the same/similar to end users, and to a certain, extent, to administrators,
there are distinct differences in the implementation. Mitel has a number of UM products and we are working to address theses differences so that our UM solutions will interwork with hosted email solutions. Depending on the specific Mitel messaging product, the rollout timing and level of support will vary."
I hope this helps.