Transitioning from a 3rd party messaging platform towards the Exchange Online service offering in Office 365 can be a challenging task especially at the enterprise scale.  Even though the Cloud has driven innovation when it comes to tools that enable feature rich coexistence and migration of disparate technologies, solution design and integration are still key components in driving functionality.

At a minimum, connecting multiple email systems requires assessing and planning for coexistence using SMTP to ensure users hosted in any platform can continue to email each other seamlessly while migration of mailbox data is ongoing.  As a trusted advisor, New Signature was recently engaged in assisting a client with transitioning from their existing IBM Notes Domino messaging system towards the Microsoft Exchange email platform with the following business requirements:

  1. Exchange 2016 would be deployed on-premises in specific geographical regions – data residency requirement
  2. Exchange Online would be hosted out of a single Office 365 tenant
  3. Inbound and outbound mail flow would be centralized on-premises –  compliance requirement
  4. Minimize changes to the existing mail platform
  5. All new mailbox provisioning was to be performed on the Notes Domino platform in the interim

Considering our requirements, we designed our mail architecture to meet the needs of the business while optimizing routing and configuration where possible and proceeded to perform the following tasks:

  1. Deployed Exchange 2016 Hybrid
    1. Using Azure Active Directory Connect (AAD Connect) we synchronized the on-premises Active Directory (AD) objects to Azure Active Directory (AAD) and enabled the Exchange Hybrid Deployment option
      1. Note: All Notes Domino mailboxes were represented in the on-premises Active Directory as mail enabled users using existing user management lifecycle processes
    2. Deployed Exchange 2016 on-premises in a Highly Available (HA) configuration as our Hybrid Servers
    3. Ran the Hybrid Configuration Wizard (HCW) to integrate the on-premises and Exchange Online platforms providing secure mail flow between the two environments
  2. Inbound Mail flow
    1. The path to inbound mail flow would continue to ingress through the mail gateway and route to Notes Domino
    2. As part of the migration process, once a mailbox migration occurred from Notes to Exchange or Exchange Online, Notes Domino would configure a Person Document and add a forwarding address pointing to the @tenant.mail.onmicrosoft.com address space (created by the HCW)
    3. Notes Domino would smart host the address space to the Exchange 2016 on-premises Hybrid endpoint
  3. Outbound Mail Flow
    1. The Outbound Connector address space from Exchange Online created by the HCW was modified to the @* address space and smart hosted to the Exchange 2016 on-premises Hybrid endpoint
      1. The @domain.com (Primary SMTP) domain was set to Internal Relay
    2. An Outbound Connector was created on the Exchange 2016 Hybrid servers with the @* address space and smart hosted to the mail gateway
      1. The @domain.com (Primary SMTP) address space was set to Internal Relay

The following diagrams depict the architecture and mail flow as designed: