Good afternoon - I have enabled DKIM on one of the domains in O365/EXO and published required Cname records in DNS.
I have a relay connector setup through Office 365 that our on-premise SMTP Server (Exchange 2013) uses to send invoices to customers.
When an email goes out directly from O365 to internet (Mailbox hosted in Exchange Online), DKIM gets applied on that email. However, when an email get relayed via on-premise SMTP (Application relay email) to O365 and then to internet, only O365 to internet hop gets DKIM applied. No DKIM stamp applied on on-premise realy (via SMTP) to O365 hop. Due to this, the recipient system see two authentication results one DKIM pass (O365 to Internet), the second one is DKIM failure (One-premise to O365 relay).
Is there anything I may be missing to get DKIM to apply to these relayed messages?
That shouldnt matter. The DKIM results from on=prem to 365 shouldnt show a failure, they should show as dkim=none since DKIM is not enabled for the on-prem servers. External recipient systems shouldnt be looking at that regardless.