The assumption that all email within an organization must run on a single platform is worth questioning. Many businesses have legitimate reasons to run different users on different email systems — cost optimization, legacy system compatibility, departmental requirements, or a phased migration that is not yet complete. A split-domain hybrid configuration makes this possible while maintaining a unified domain and seamless mail flow between platforms.
What Is Split-Domain Email?
In a split-domain configuration, multiple email platforms handle mailboxes for the same domain simultaneously. User A on @yourcompany.com might have their mailbox on StrataMail while User B on the same domain has their mailbox on Microsoft 365. From the outside — and from each other's perspective — both users appear identical: same domain, same email format, fully reachable from anywhere.
The mail routing infrastructure handles the behind-the-scenes complexity. Inbound mail for User A routes to StrataMail's servers. Inbound mail for User B routes to Microsoft's servers. Internal mail between User A and User B routes correctly between platforms. Spam filtering can be applied centrally before mail reaches either platform.
Why Organizations Use Split-Domain Configurations
- Cost optimization: Microsoft 365 Business Premium costs significantly more per user than StrataMail. Organizations can keep high-volume power users on StrataMail at lower cost while putting a subset of users who need M365-specific features (Teams, SharePoint, advanced calendar) on M365 licenses.
- Phased migrations: Moving an entire organization to a new platform in a single cutover is high-risk. A split-domain hybrid lets you migrate in waves — validating the new platform with a pilot group before expanding — without disrupting the users who remain on the current system.
- Departmental requirements: Some departments may require Exchange/Outlook-specific features while others function perfectly with StrataMail. A hybrid serves both groups under the same domain.
- Existing filter integration: Organizations with an existing spam filtering investment can route all mail — regardless of destination platform — through their existing filter before splitting to the appropriate mail server.
StrataMail + Microsoft 365
Infinity Data Center's StrataMail + M365 hybrid configuration routes StrataMail users and M365 users under the same domain with unified mail flow. Inbound mail arrives at a central routing point — typically StrataMail or a spam filtering gateway — and is delivered to the correct platform based on recipient. M365 users' outbound mail can optionally route through StrataMail's SMTP infrastructure for consistent spam filtering and delivery reputation management.
SpamWeeder Premium or another Infinity Data Center spam filter can be placed in front of both platforms simultaneously, providing a single pane of glass for filtering policy and quarantine management across both M365 and StrataMail users.
StrataMail + Google Workspace
The StrataMail + Google Workspace split-domain configuration follows the same architecture — StrataMail handles one set of mailboxes, Google Workspace handles another, both under the same domain. Organizations moving from Google Workspace to StrataMail (or vice versa) use this configuration during the transition period. Organizations with specific users who require Google Workspace's collaboration tools while others need only standard email use it as a permanent cost-optimization strategy. Contact our team to discuss a Google Workspace + StrataMail split-domain configuration.
Unified Spam Filtering Across Both Platforms
One of the operational advantages of a split-domain configuration managed by Infinity Data Center is the ability to apply unified spam filtering across both platforms. Rather than configuring spam policies separately in M365's Defender and separately in StrataMail, a central gateway filter — SpamWeeder Premium, VIPRE, or Proofpoint Essentials — sits upstream of both mail systems. All inbound mail is filtered at the gateway, then routed to the correct platform. This simplifies policy management and ensures consistent protection regardless of which platform each user's mailbox lives on.
How Infinity Data Center Sets It Up
Setting up a split-domain hybrid involves DNS configuration, MX routing rules, and — depending on the platforms involved — connector configuration on the receiving mail systems. Infinity Data Center's engineering team designs and configures the full routing architecture, tests message flow between platforms in both directions, and validates spam filtering integration before cutover.
The process typically takes one to three days depending on the complexity of the environment and the number of platforms involved. Infinity Data Center also provides documentation of the configuration for your IT records and can train your team on how to add new users to the correct platform. Contact us or call 866.790.4678 to discuss your split-domain requirements.