Exchange Server, Exchange Online, hybrid coexistence, mail flow, and email security handled by engineers who work in production environments.
Email migrations fail when the pre-migration work is skipped. DNS TTLs not lowered before cutover. MX records changed before mailboxes are fully synced. Autodiscover pointing to the wrong endpoint. Public folder migration started after business hours on a Friday. These are not exotic failure modes — they show up on almost every migration that was quoted too cheaply or handed to someone who hadn't done it before.
This practice runs Exchange migrations with a written cutover checklist, a tested rollback plan, and DNS changes made in a specific order that preserves mail flow continuity throughout. The goal is zero lost email and zero unplanned downtime.
Hybrid Exchange is often oversold. For organizations moving entirely to Exchange Online, a full hybrid deployment adds months and complexity that a well-executed cutover migration doesn't require. Hybrid is the right choice when you need free/busy calendar sharing between on-premises and cloud users during a staged migration, or when regulatory requirements mandate that certain mailboxes stay on-premises permanently.
Express Hybrid — introduced to simplify the configuration — is appropriate for smaller organizations. Full Hybrid provides more control over mail routing and is the correct choice for organizations with complex mail flow, existing third-party journaling, or multiple Active Directory forests. The assessment conversation covers which option is appropriate for your situation before any work begins.
Moving mailboxes to Exchange Online and leaving SPF, DKIM, and DMARC in whatever state they were in before migration is a common mistake. Exchange Online's outbound IP addresses are different from your on-premises server. SPF records that don't include Microsoft's sending ranges result in legitimate email being marked as spam by recipient mail servers. The post-migration hardening phase of every project includes a full email authentication audit and configuration.
For organizations targeting DMARC enforcement — increasingly required for sending to Gmail and Yahoo at volume — the path from p=none to p=reject involves resolving every authorized sending source, including marketing platforms, CRMs, transactional email services, and third-party connectors. That inventory and alignment work is part of this service.
With proper planning, no. The cutover window involves a brief period where new email is held by the MX record's previous destination while DNS propagates. This is managed by lowering TTLs 48 hours before cutover and coordinating the MX change with the final mailbox sync. Mail is never lost — it's queued and delivered after propagation completes.
Public folders are one of the more complex parts of Exchange migration. They can be migrated to Exchange Online public folders (appropriate for active usage), converted to shared mailboxes (better for archived content), or decommissioned if usage data shows they aren't actively accessed. The right choice depends on actual usage patterns, which are assessed during the planning phase.
A cutover migration for an organization under 150 mailboxes typically takes 2–3 weeks from assessment to completed cutover, assuming Active Directory is in reasonable health. Staged or hybrid migrations with legacy infrastructure take 6–10 weeks. Public folder migrations add time proportional to data volume and complexity.