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Migrate Google Workspace to Zimbra

This guide walks through the full process of migrating mailboxes from Google Workspace (formerly G Suite) to Zimbra hosted on InteSys, preserving folders, labels, filters, calendars, and contacts — with zero downtime for end users.

Step 1: Prerequisites

Before you begin, make sure you have:

  • Administrator access to the Google Workspace console (admin.google.com).
  • A list of the mailboxes to migrate (CSV with address, name, group/OU, and mailbox size).
  • DNS access for the domain (for the final MX record cutover).
  • InteSys Zimbra hosting already provisioned — if you haven't signed up yet, follow the Hosting Setup Guide.

Recommended window

Plan for a 3- to 5-business-day window for mailboxes up to 50 GB. Sync runs in parallel with normal usage — users keep receiving email in Google until the cutover.

Step 2: Volume Assessment and Window Planning

Go to admin.google.com > Reports > User usage and export storage consumption per mailbox. Sort mailboxes into three tiers:

Tier Size Strategy
Light < 5 GB Individual migration, 1–2 h
Medium 5–30 GB Batches of 5 mailboxes, overnight
Heavy > 30 GB Dedicated migration, per-user window

With this breakdown, the InteSys assisted migration team sizes batches and windows so productivity is never impacted.

Step 3: Google Service Account and OAuth Scopes

InteSys uses a Google service account with domain-wide delegation to read mailboxes through the Gmail/EWS API — no individual user passwords required.

  1. In admin.google.com > Security > API controls > Domain-wide delegation.
  2. Add the Client ID provided by InteSys with the following OAuth scopes:
    • https://mail.google.com/
    • https://www.googleapis.com/auth/calendar.readonly
    • https://www.googleapis.com/auth/contacts.readonly
  3. Save and allow up to 30 minutes for permissions to propagate.

Read-only scopes

Delegation is strictly read-only. No data is modified or deleted from Google Workspace during the migration — the source environment stays fully intact.

Step 4: Provisioning the Zimbra Destination

In the InteSys Customer Portal, under Services > Email Hosting > Mailboxes:

  1. Import the CSV with the user list (the same one from Step 2).
  2. Set quotas based on the plan you purchased (Starter 2 GB, Business 10 GB, Enterprise 25 GB or higher).
  3. Generate temporary passwords — users will receive them through a secure channel on cutover day.

Bulk provisioning creates every mailbox in seconds. Aliases, groups, and distribution lists can be imported in the same step.

Step 5: Parallel IMAP Migration

With the service account authorized and the Zimbra mailboxes ready, the InteSys migration tool kicks off an incremental copy:

  1. First pass: full copy of all folders, messages, and attachments. Gmail labels are converted into Zimbra folders (INBOX/Clients/Project-X).
  2. Delta syncs: every 30 minutes, only messages that are new or changed since the last pass are copied.
  3. Filters and rules: Gmail filters are converted into Zimbra Sieve filters wherever an equivalent exists.

Throughout this phase, users keep working in Google Workspace as usual. Incoming mail is replicated to Zimbra within minutes.

Labels vs folders

A message with multiple Gmail labels becomes one copy per matching folder in Zimbra. This preserves organization but can slightly inflate storage usage — plan for roughly +10% on top of the quota.

Step 6: Calendar and Contact Migration

Calendars and contacts migrate over CalDAV/CardDAV, also in parallel:

  • Primary and secondary calendars from Google Calendar → Zimbra calendars with matching colors and sharing permissions.
  • Recurring events, invitees, and attachments are preserved.
  • Personal contacts and groups from Google Contacts → Zimbra address book.
  • Corporate directory (Google Directory) → Zimbra GAL (Global Address List).

After the cutover, clients configured via CalDAV/CardDAV keep working — see the Calendar and Contacts Guide for reconfiguration details.

Step 7: MX Cutover and Final Sync

On the agreed day:

  1. T-0: run the final delta sync (capturing the last few minutes of mail).
  2. T+5 min: change the MX records in your DNS to point to mx1.intesys.io and mx2.intesys.io with a low TTL (300s).
  3. T+10 min: new messages are delivered directly to Zimbra.
  4. T+24 h: a final sync captures any stragglers that still landed in Google during DNS propagation.

See the DNS Configuration Guide to set up SPF, DKIM, and DMARC on the new destination.

Step 8: Post-Migration

Let your users know:

  • Zimbra webmail: https://mail.intesys.io — log in with the full email address and temporary password (password change required on first login).
  • iPhone / Android: reconfigure the account as Exchange ActiveSync pointing to mail.yourdomain.com. Full details in the ActiveSync Guide.
  • Outlook: remove the old Google account and add the new one via autodiscover or ActiveSync.
  • Diagnostic tools: use the ActiveSync Test if authentication fails.

For the first 30 days after cutover, keep the Google Workspace mailboxes active as a safety net — after that, the plan can be safely canceled.

Ready to leave Google Workspace without losing history? InteSys business email plans include free assisted migration — or head over to the dedicated migration hub to talk to the team.