Microsoft 365 is a powerful platform — but at $12–$22 per user per month for Business plans, the licensing 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 M365 + StrataMail split-domain configuration lets organizations get the best of both: M365 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 M365 suite. Others — field staff, contractors, administrative roles — need email and little else. Paying full M365 licensing for every user when half of them only use email is a significant overspend. The hybrid configuration right-sizes licensing: M365 licenses for users who use M365 features, StrataMail for users who need email.
Secondary use cases include phased migrations (using the hybrid as a transitional state while moving users from M365 to StrataMail or vice versa) and organizations that want an independent email backup — users whose primary mailbox is on M365 can also have a StrataMail account as a continuity fallback.
Architecture Overview
The M365 + 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. M365 mailboxes receive mail through Microsoft's connectors. StrataMail mailboxes receive mail through Infinity Data Center's mail servers. Both groups of users share the same @yourcompany.com domain.
How Mail Routing Works
The routing decision happens at the spam filter or mail gateway layer, before mail reaches either platform. The gateway maintains a routing table that maps each recipient address to their mail platform. When an inbound message arrives for alice@yourcompany.com (StrataMail) it is forwarded to StrataMail's servers. When a message arrives for bob@yourcompany.com (M365) it is forwarded via connector to Microsoft's Exchange Online infrastructure.
Internal mail between a StrataMail user and an M365 user routes through the same gateway — Alice's email to Bob routes outbound through StrataMail, through the gateway, and into M365'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 M365 Defender policies for M365 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, whitelist/blacklist rules, and filtering reports cover both user populations from a single interface.
MX Backup & Continuity for Hybrid
StrataMX Backup and email continuity services work with the hybrid configuration — protecting inbound mail and user access regardless of which platform each user's mailbox lives on. When the hybrid routing gateway or either mail platform has an outage, StrataMX Backup queues inbound mail and the continuity portal provides emergency access for affected users. This is particularly valuable for M365 users who might otherwise have no fallback when Microsoft has a service incident.
Setup by Infinity Data Center
Infinity Data Center engineers the full M365 + StrataMail hybrid configuration: DNS MX records, gateway routing rules, M365 inbound connector configuration, StrataMail routing, 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.
Contact our team to discuss your M365 environment and hybrid requirements, or call 866.790.4678.