[Battle Hymn of the Republic]

Exchange Server is not the gateway, but the email platform. All email goes through an MTA (Message transfer agent) if it's on premise. There is a tech vendor who may have these IRS emails, depending on which MTA.

I am no professional on this, but know a lot.

[mmichaels1970]

All email goes through an MTA (Message transfer agent) if it's on premise.

Isn't that what the Microsoft Exchange MTA Stacks service does? I just have Exchange and a static IP address with an MX record. I don't have anything else but an Adtran router between my mail server and the internet.