User A(Office 365) & User B (Office365 & External), Whenever User A Sends Mail to User B, It should be delivered External User B account from there it has to be forwarded to Office365 User B Mailbox, However default it will be delivered to User B Mailbox in Office365 Domain.com Hosted with Office365 & Some other provider Internal Mails should be routed to Other Provider & Needs to forwarded to Office365
Internal domains look up happens within Office365 server hence mail delivery fails is expected.
Since the same office 365 tenant has User B mailbox enabled, Mails will not be delivered to External Servers.
We suggest you to create a new Outbound Connector for your domain as follows:
- Type : Partner
- Connection : Opportunistic TLS
- Scope : Use for Criteria Based Routing (CBR)
- Outbound Delivery : MX record associated with the recipient domain
Once created, Go ahead & create a rule as follows:
- If the message...recipients’ s address domain portion belongs to any of these domains: yourdomain.com
- Do the following...Route the message using the connector named "Created Connector"
Note : If the DomainType Set to InternalRelay, Rules will take high precedance.