If you are an Exchange Online or Exchange Online Protection (EOP) customer and you have configured connectors, this post contains important information that might impact your organization. To make ...
Updated Jul 01, 2019
Version 2.0
Blog Post
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Important notice for Office 365 email customers who have configured connectors
@Carolyn Liu
In this example contoso.com is a domain in an O365 tenant, subdomain.contoso.com is also a domain in the same O365 tenant but the tenant is configured as an internal relay for subdomain.contoso.com. Any messages to @subdomain.contoso.com recipients that cannot
be delivered within O365 will be relayed to server1.subdomain.contoso.com which is authoritative for subdomain.contoso.com.
The sender can be anyone including @contoso.com, O365 would just be used as the ingress/egress points for subdomain.contoso.com so we can provide inbound message hygiene and authenticated email relaying.
The way I read the document we would need a certificate on server1.subdomain.contoso.com.