DKIM for O365 Relay (On-premise SMTP server)

Jan Anne Bijlsma 

You're right.
On-Prem Exchange SMTP relay to O365 DKIM=none

On-Prem Exchange SMTP relay to External such as gmail DKIM=pass

My issue, is ExchangeOnlineProtection is marking On-Prem to O365 as SPAM (5). I figured that by adding DKIM the spam rating would likely reduce.

Not wanting to whitelist the on-prem exchange server for the SPAM filter, I'll look at switching from anonymous relay to authenticated to try and lower the spam confidence level...