{"id":74452,"date":"2026-10-29T14:21:22","date_gmt":"2026-10-29T21:21:22","guid":{"rendered":"https:\/\/cirasync.com\/?p=74452"},"modified":"2026-10-29T14:21:22","modified_gmt":"2026-10-29T21:21:22","slug":"office-365-tenant-to-tenant-migration-gal-sync","status":"publish","type":"post","link":"https:\/\/cirasync.com\/es\/blog-articles\/office-365-tenant-to-tenant-migration-gal-sync\/","title":{"rendered":"Office 365 Tenant-to-Tenant Migration: How to Keep GAL and Company Contacts Synced\u00a0"},"content":{"rendered":"

Moving users to a new Microsoft 365 tenant is more than a mailbox project. IT teams also need to account for how employees find colleagues, access shared business contacts, and identify incoming calls on their smartphones. A successful mailbox move does not automatically mean every directory entry, contact workflow, and mobile address book is ready in the destination environment.<\/span>\u00a0<\/span><\/p>\n

Quick answer: Microsoft supports moving user-visible mailbox content, including personal contacts, through its cross-tenant Exchange Online mailbox migration process. But the Global Address List (GAL) is built from directory recipient objects, not simply copied as a personal contact folder. Before cutover, confirm which directory objects must exist in the destination tenant. After cutover, test GAL search, shared contacts, and smartphone contact sync separately.\u00a0<\/span>\u00a0<\/span><\/p>\n

This guide explains what changes during tenant migration and gives Microsoft 365 administrators a practical contact-continuity plan for before, during, and after the move.<\/span>\u00a0<\/span><\/p>\n

<\/span>What is Office 365 tenant-to-tenant migration?<\/span><\/h2>\n

Office 365 tenant-to-tenant migration, also called Microsoft 365 cross-tenant migration, is the process of moving users and selected services or information from one Microsoft 365 organization to another. It commonly forms part of mergers, acquisitions, divestitures, reorganizations, or tenant consolidation.<\/span>\u00a0<\/span><\/p>\n

In an Exchange Online mailbox migration, administrators prepare source and target organizations, establish the required permissions and relationships, provision the appropriate target objects, and move eligible mailboxes in planned batches. Microsoft documents this workflow and its licensing requirements. Other workloads, such as SharePoint, Teams, and identity configurations, have their own migration considerations.\u00a0<\/span>\u00a0<\/span><\/p>\n

The mistake to avoid is treating mailbox migration, directory preparation, GAL visibility, and phone contact synchronization as one operation. Each has different requirements and a different way to verify success.<\/span>\u00a0<\/span><\/p>\n

<\/span>What happens to contacts and the GAL during a tenant migration?\u00a0<\/span><\/span><\/h2>\n

The answer depends on the kind of contact data involved. A contact stored in an employee’s mailbox is not the same thing as an organization-wide GAL entry, a shared contact, or a contact already saved on a phone.<\/span>\u00a0<\/span><\/p>\n\n\n\n\n\n\n\n\n\n
Contact or directory data<\/span>\u00a0<\/span><\/td>\nWhat administrators need to know<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Personal mailbox contacts<\/span>\u00a0<\/span><\/td>\nContacts stored as user-visible content inside a mailbox are included in supported cross-tenant Exchange Online mailbox moves. Local PST contacts or other client-only address books are separate.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Global Address List entries<\/span>\u00a0<\/span><\/td>\nThe GAL itself is not copied as a mailbox contact folder. The destination GAL is generated from mail-enabled recipient objects and Exchange address-list visibility in the target tenant.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Distribution lists and mail contacts<\/span>\u00a0<\/span><\/td>\nThese are not part of mailbox data migration. Microsoft advises creating the required objects in the target tenant separately.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Public Folder contacts<\/span>\u00a0<\/span><\/td>\nPublic folders are not included in Microsoft FastTrack cross-tenant mailbox migration and require a separate migration or replacement plan.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Shared or departmental contacts<\/span>\u00a0<\/span><\/td>\nFirst identify where they are stored. If they live in another mailbox, Public Folder or separate contact source, validate that source’s migration path and permissions separately.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n
Smartphone contacts and caller ID<\/span>\u00a0<\/span><\/td>\nThese are not validated by a successful mailbox migration. Test native phone contacts and caller ID separately after the destination contact-sync configuration is ready.<\/span>\u00a0<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u00a0<\/span>For example, a migrated employee may see their own personal contacts in Outlook but still be unable to find every coworker in the destination GAL. Another employee might find a colleague through Outlook search, yet still see an unknown phone number on an incoming call because that colleague has not been synchronized into the phone’s contacts.<\/span>\u00a0<\/span><\/p>\n

<\/span>Before migration: prepare the directory and contact data<\/span><\/h2>\n

Contact continuity begins before the first migration batch. Document the current state so the team knows what must be transferred, recreated, synchronized, or tested.<\/span>\u00a0<\/span><\/p>\n

    \n
  1. Inventory the source GAL. Identify mailboxes, mail users, mail contacts, distribution groups, shared mailboxes, and any custom address lists that employees depend on. Record critical phone numbers and other attributes that support daily communication.<\/span>\u00a0<\/span><\/li>\n
  2. Separate personal and organizational contacts. Personal mailbox contacts may move with the mailbox through a supported Microsoft migration process. Other address book resources may need dedicated preparation.\u00a0<\/span>\u00a0<\/span><\/li>\n
  3. Map the destination directory. Confirm how employees and external contacts will appear as mail-enabled recipients in Exchange Online. Check expected email addresses, display names, phone attributes, and GAL visibility.<\/span>\u00a0<\/span><\/li>\n
  4. Identify contact consumers. Include field teams, sales staff, help desks, executives, and any group that depends on smartphone caller ID or offline access to saved business contacts.<\/span>\u00a0<\/span><\/li>\n
  5. Document current sync rules. If an organization uses automated GAL or shared-contact synchronization, capture the source, target users, contact folders, filters, and sync ownership. Plan how those settings will be changed when users move.<\/span>\u00a0<\/span><\/li>\n
  6. Run a pilot. Migrate a representative user group, including people with personal contacts, shared contact access, and mobile devices. Confirm both data movement and everyday contact usability before expanding the rollout.<\/span>\u00a0<\/span><\/li>\n<\/ol>\n

    Microsoft requires specific target mail user preparation and cross-tenant migration licensing for its native mailbox moves. Check Microsoft’s current prerequisites for your migration approach instead of assuming permissions, provisioning, and licensing are already in place.\u00a0<\/span>\u00a0<\/span><\/p>\n

    <\/span>During migration: keep company contacts accessible<\/span><\/h2>\n

    A staged migration can leave colleagues split between source and target tenants for days or weeks. Mail routing and mailbox access are important, but so is the ability to find the right person in the organization.<\/span>\u00a0<\/span><\/p>\n

    For every migration batch, use a documented communication and verification process:<\/span>\u00a0<\/span><\/p>\n