Microsoft 365 is a powerful platform — but at Business-plan licensing for every user, the cost adds up quickly for organizations where many users need only standard email. StrataMail provides professional, secure, managed email at a fraction of that cost. The Microsoft 365 + StrataMail split-domain configuration lets organizations get the best of both: Microsoft 365 for users who need Teams, SharePoint, and full Exchange integration, and StrataMail for users who need reliable, professional email at a lower per-seat cost.
Why M365 + StrataMail?
The core use case is cost efficiency without capability compromise. In a typical organization, some users — executives, sales, operations leads — benefit from the full Microsoft 365 suite. Others — field staff, contractors, administrative roles — need email and little else. Paying full Microsoft 365 licensing for every user when half of them only use email is a significant overspend. The hybrid configuration right-sizes licensing: Microsoft 365 licenses for users who use Microsoft 365 features, StrataMail for users who need email.
Secondary use cases include phased migrations (using the hybrid as a transitional state while moving users from Microsoft 365 to StrataMail or vice versa) and organizations that want an independent fallback when Microsoft has an incident — see MX backup and continuity below.
Estimate the Cost of Your M365 + StrataMail Split
Most mailboxes do not need a full Microsoft 365 license. Move the sliders below to see the right-sizing saving — keep the seats that need Microsoft, move the rest to StrataMail, and compare against licensing every user on one platform.
Architecture Overview
The Microsoft 365 + StrataMail hybrid places both mail systems under the same domain with a shared MX entry point. Inbound mail arrives at a central routing layer — typically a spam filtering gateway managed by Infinity Data Center — where it is filtered and then routed to the correct platform based on the recipient's mailbox location. Microsoft 365 mailboxes receive mail through Microsoft's connectors. StrataMail mailboxes receive mail on a StrataMail VPS, which is where the per-address routing rules for a split domain live. Both groups of users share the same @yourcompany.com domain.
How Mail Routing Works
The routing decision happens at the routing layer, before mail reaches either platform. Routing entries map each recipient address to its mail platform, and a single address can be overridden to a different server than the rest of its domain. When an inbound message arrives for alice@yourcompany.com (StrataMail) it is delivered to StrataMail. When a message arrives for bob@yourcompany.com (Microsoft 365) it is forwarded via connector to Microsoft's Exchange Online infrastructure.
Internal mail between a StrataMail user and a Microsoft 365 user follows the same routing — Alice's email to Bob leaves StrataMail and enters Microsoft 365's incoming path for Bob. The routing is seamless and transparent to both users.
Centralized Spam Filtering
One of the most practical advantages of managing both platforms through Infinity Data Center is centralized spam filtering. Rather than managing Microsoft Defender policies for Microsoft 365 users and StrataMail filtering for StrataMail users separately, a single upstream gateway — SpamWeeder Premium, VIPRE, or Proofpoint Essentials — applies consistent filtering policy to all inbound mail before it reaches either platform. Quarantine management, allow and block rules, and filtering reports cover both user populations from a single interface.
MX Backup & Continuity for Hybrid
StrataMX Backup and StrataMail Email Continuity work with the hybrid configuration — protecting inbound mail and user access regardless of which platform each user's mailbox lives on. When either mail platform has an outage, StrataMX Backup queues inbound mail for up to 30 days, and StrataMail Email Continuity gives affected users branded webmail access in the meantime. This is particularly valuable for Microsoft 365 users who might otherwise have no fallback when Microsoft has a service incident.
Setup by Infinity Data Center
Infinity Data Center engineers the full Microsoft 365 + StrataMail hybrid configuration: DNS MX records, routing rules on your StrataMail VPS, Microsoft 365 inbound connector configuration, spam filter integration, and testing of mail flow in all directions. Setup documentation is provided for your IT records. Infinity Data Center supports ongoing management of the hybrid routing configuration as users move between platforms.
See StrataMail Routing for Microsoft 365 at Infinity Data Center, contact our team to discuss your Microsoft 365 environment and hybrid requirements, or call 866.790.4678.