Contrary to the documentation for Exchange 2016 and Exchange 2019, in our Exchange 2016 environment the message-ID does not follow this statement : “For messages created in Exchange, the value is in the format <GUID@ServerFQDN>” Instead all message-ID’s are constructed as such <GUID@Primary_SMTP_Address_of_Sending_Object>. This is only an issue for my company as we have (for historical reasons that we are slowly addressing) multiple mail environments not running Exchange that are also authoritative for our primary domain. So any routing rules in place that across our disparate email environment that evaluate on the message-ID are getting thrown off by the fact that our Exchange environment does not follow the published documentation for message-ID’s. Does anyone know why this would be the case and how to fix it?
