dears,
I'm planning to upgrade our mail system from 2013 to 2019, so I need your help to set a plan to perform this upgrade depend on our existing environment as below :
1- Domain Server 2012 R2 .
2 - Exchange 2013 with CU22 (2 Mail Box Server with DAG) .
3 - 2 Cas Server (With Zen Load Balance ) .
4 - 1 Archiving Server for mail box.
so I need your help to perform this upgrade without stopping the existing mail system .