Able to use cloud users/mailboxes with Hybrid?

Occasional Contributor



  • 40 Production cloud users existing in O365 tenant on
  • MX points to EOP and specific transport rule catches email from senders and forces back out EOP instead of going on prem (per requirement)
  • On Prem 2013/2016 environment with
  • MX for points on prem
  • HCW executed successfully for
  • Requirement for centralized mail transport




When both Hybrid connectors are enabled in O365, email sent to hits the transport rules in O365 then gets forwarded to Hybrid Connector to push all mail to on prem. Mail never reaches cloud mailbox of If I disable the Hybrid Connector to on prem it works fine. 


I would have thought incoming mail to O365 for would have went through transport rules, then looked for mailbox, then forward to connector, but this does not seem to be the case. Is there any way to properly incorporate the existing cloud only mailboxes & users (users not sync with AAD) into this Hybrid? MS told me no. 

2 Replies

If i understand your situation correctly you do not have to do anything with the transport rules. Just remove te hybrid and keep your users from domain a and b seperated.

What you can do is

Set the mx for domain a to O365 EXO

Set the mx for domain b to EXOP


You can also create a Hybrid set all MX records to O365 EXO. After this migrate the onprem users to O365 EXO and use domain B as Suffix. Make sure the production cloud users have suffix A in O365 EXO.


I only have a few questions:

Do the production cloud users also have a onprem AD account in the same AD as the other users?

What is the meaning of the domain.

What is the final goal you want to reach?

OP: What you have described you cannot do. Incoming email hits mail flow rules and is routed onprem. Remove this mail flow rule and it will hit the mailboxes first. Ensure domain-a in EXO is listed as "internal relay" as the accepted domain value and then it will automatically route emails to onprem domain-a users. You cannot, with centralized mailflow, then route the EXO users out to internet and everything else via onprem create own connectors and not HCW connectors, but that is going to be tricky

Brian Reid, MVP