Microsoft 365 Admin - Accepted Domains

[tangotech]

Can someone advise which setting is best and why?

 

Within Microsoft 365 Admin Center > Exchange Admin > Mail Flow > Accepted Domains > Primary Domain

 

 

 

 

What settings to set?.... Authoritative or Internal Relay?

[chaplic]

If all your email is inside O365, Authoritative. If your email goes to on prem first then O365, authoriative. If you take email from internet to O365 then pump some to other systems, internal relay.

 

 

Else what will happen is if someone emails an address that doesn't exist, O365 will pass it down whatever connector it is appropriate, probably just to the internet. So it will NDR but only because an email loop will be detected

[tangotech]

Yes, all our emails are in M365.

 

I should probably update from relay to auth ... however, does anyone know if changing this will causes an issue?

[chaplic]

send an email from hotmail or simliar to [email protected] - it will NDR but probably take a few minutes and if you read the NDR you'll see it says message loop detected

 

Make the change to authoriative, give it 10 mins, repeat the test and NDR will happen almost immediately.

 

So it's not a massive win and I've seen plenty orgs with the wrong setting run quite happily, but if you dont have hybrid or any other system with your domains email should be a no drama tidyup.