Microsoft 365 Migration
with Zero Email Downtime
A San Antonio law firm migrated from an on-premises Exchange server to Microsoft 365 with zero email downtime. IDENETY MSP handled DNS cutover, mailbox migration, Entra ID configuration, and MFA rollout — completed over a weekend.
The Challenge
A San Antonio law firm with 28 attorneys and staff was running on an aging on-premises Exchange 2013 server that had reached end-of-life. The server required hardware replacement, and the firm's IT budget was better spent on Microsoft 365 licensing than on new server hardware. The critical requirement: zero email downtime. For a law firm, email is mission-critical — a single hour of email downtime during business hours could mean missed court deadlines or client communications.
Migration Timeline
Discovery & Planning
Inventoried 28 mailboxes, 4 shared mailboxes, and 3 distribution lists. Documented DNS records, MX configuration, and Exchange server settings. Created a detailed migration runbook with rollback procedures.
Migration Kickoff
Initiated mailbox migration using Microsoft's hybrid migration tool. Began syncing mailbox data to M365 while Exchange remained live. Users continued working normally with no disruption.
Mailbox Sync Complete
All 28 mailboxes synced to M365. Verified mailbox integrity and item counts. Configured Entra ID (Azure AD) with all user accounts and security groups. Deployed Intune MDM policies.
MFA Rollout
Enrolled all 28 users in Microsoft Authenticator MFA. Configured Conditional Access policies requiring MFA for all sign-ins. Tested access from multiple devices and locations.
DNS Cutover
Updated MX records to point to Microsoft 365. Updated SPF, DKIM, and DMARC records. Decommissioned Exchange server send connectors. Zero email downtime — mail flow continued uninterrupted.
Verification & Cleanup
Verified mail flow from all 28 mailboxes. Tested Teams, SharePoint, and OneDrive access. Confirmed Intune device compliance. Decommissioned on-premises Exchange server.
What Was Delivered
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