Legacy production messaging
The existing Kerio environment remained operationally critical until every mailbox had been migrated and accepted in Exchange Online.
Case study 04 / Clinical research
Kerio Connect to Exchange Online.
Migrating 150 mailboxes from legacy Kerio Connect email servers to Exchange Online over 30 days, with dual delivery maintaining mail flow throughout the transition.
150 mailboxesMoved to Exchange Online
30 daysControlled migration period
0 downtimeDual delivery maintained
Modernise the messaging platform without interrupting mail flow.
The clinical research organisation depended on legacy Kerio Connect servers for business email. Moving 150 users to Exchange Online required coexistence between the old and new platforms while mailbox migrations progressed.
Dual delivery
Mail routing was configured to support delivery during coexistence, allowing users to transition in controlled groups without a single all-or-nothing cutover.
Zero-downtime migration
All 150 mailboxes were moved over a 30-day period while email services remained available to the business.
Architecture & delivery
Coexistence separated mailbox movement from business risk.
The migration design allowed Kerio Connect and Exchange Online to operate during the transition. That created time to move and validate mailboxes in stages while maintaining a working mail path.
01
Messaging discovery
Reviewed the Kerio Connect environment, mailbox population, domains and mail-flow dependencies affecting migration.
02
Exchange Online preparation
Established the Microsoft cloud destination and the configuration required to receive migrated users.
03
Dual-delivery design
Configured mail delivery to operate across the legacy and destination systems during the coexistence period.
04
Staged mailbox movement
Migrated 150 mailboxes across a 30-day programme instead of concentrating production risk into one event.
05
Cutover validation
Confirmed mailbox access and mail flow as users transitioned, then completed the move into Exchange Online.
Thirty days of controlled change, not thirty days of disruption.
Each stage protected the ability to send and receive business email while the migration advanced toward the final Exchange Online state.
Map the mail environment
Identify users, domains, routing and the dependencies tied to the Kerio platform.
Establish coexistence
Ready Exchange Online and configure dual delivery across both production systems.
Move in controlled waves
Transfer mailboxes progressively and validate the user experience throughout the 30-day period.
Finish the transition
Confirm all 150 mailboxes in Exchange Online and remove dependence on the legacy mail platform.
Delivered outcome150 /
30 days
30 days
Every mailbox migrated without a production outage.
Exchange Online introduced while the business kept communicating.
The organisation completed its transition from Kerio Connect to Exchange Online without downtime. Dual delivery gave the project a controlled coexistence period while 150 mailboxes moved over 30 days.
This approach reduced the operational consequence of each migration wave and allowed mail flow to remain available throughout the programme.
- Legacy Kerio Connect source
- Exchange Online destination
- 150 mailboxes migrated
- Dual delivery and zero downtime
Related case studies.
Messaging migration often forms part of a wider Microsoft 365, identity or merger programme.
Protect mail flow
Planning a move to Exchange Online?
Define coexistence, routing and validation before production mailboxes begin to move.
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