Exchange message transport & routing has at times been a bit challenging to understand. Whether it was the X400 based Mail Transport Agent (MTA), Open Shortest Path First (OSPF) based routing in Exch...
Updated Aug 23, 2023
Version 9.0
Blog Post
Hello Arindam_Thokder
I have the following hybrid mailflow issue :
Context:
Exchange 2010 infrastructure
. domains : @subdomA.domain.com / @subdomB.domain.com / @subdomC.domain.com / ...
. Hybrid is being set up with a different EXO tenant for each subdomain. (subdomA.domain.com mailboxes have already been moved to EXO)
. MX still points to on-prem for all domains. (Through third party filtering)
. on-prem send-connector being created for each EXO tenant/domain.
Exchange Online tenants
. @subdomA.domain.com tenant has both inbound and outbound connectors, allowing hybrid mailflow with mailboxes still on-prem
. @subdomB.domain.com tenant is being set up for hybrid migration, with similar connectors.
Issue :
After creating inbound connector (IP based) on @subdomB.domain.com tenant, mailflow from on-prem subdomB to EXO subdomA is attributed by EXO as originating to subdomainB, which causes the mail to loopback to on-prem (following outbound connector) instead of being delivered to subdomA tenant.
What solution would you recommend here ? Changing MX (or routing after third party filtering) to EXO instead of on-prem ? Not using inbound connectors in EXO and whitelist cross-prem emails another way ?
Any help welcome 🙂