you can use Late binding on your code:
Dim olApp As Object
Dim olMail As Object
Set OlApp = CreateObject("Outlook.Application")
Set OlMail = olApp.CreateItem(0)
if there are outlook constants (ie, olMailItem), inspect it in immediate window to get the value:
once you completed the conversion, you may safely remove reference to outlook.
to be able to change the reference, one should know which version of office he is using (x86 or x64) and 15 or 16.
since the path to these files (therefore the reference path) is not same.