Zimbra to Office 365 Migration Guide


  1. How to migrate mailboxes from Zimbra to Office 365
    1. Cutover migration
      1. Cutover migration benefits
      2. Cutover migration considerations
  2. Security
  3. Performance
  4. Mail migration scope
    1. What can be migrated
    2. Migration limitations
    3. Considerations
    4. Audience
  5. Pre-migration configuration
    1. Before you start
    2. Set up an Office 365 account with impersonation privileges
  6. Use the Cloudiway platform to migrate your mail
    1. Create your source and target connectors
    2. Create a partial archive from a normal inbox
    3. Configure the global settings for migration
    4. Import or create your users
      1. Option 1: CSV import
      2. Option 2: Import Users tool
      3. Option 3: Single user creation details
    5. Activate and monitor your migration
    6. Migrate permissions globally
  7. Troubleshooting

1. How to migrate mailboxes from Zimbra to Office 365

Cloudiway’s mail migration solution helps businesses perform elaborate technical migrations through a simple SaaS interface. As a result, mail migrations require no additional software installation or overhead, and migrations can be performed securely and quickly.

The Cloudiway platform is flexible enough to support all types of migration paths. Your migration strategy will depend on your business setup, type and size. Whichever migration path you choose, Cloudiway provides all the essential features including automatic account provisioning, license assignment, archive migration, mail routing and calendar coexistence (free/busy scheduling).

Two of the most common migration strategies are cutover and staged migrations. Cutover strategies involve migrating all mailboxes over a weekend, ready for your users on Monday morning. Staged strategies provide more flexible migration options, as discussed below.

1.1 Cutover migration

You migrate everybody over a weekend and perform a single migration pass. This strategy is the simplest to implement. After you have switched your MX records to point to the new system, you start mailbox migration.

Cutover migration is, therefore, a strategy where the entire company is switched at the same time.

1.1.1 Cutover migration benefits

  • Fastest, simplest form of migration.
  • Your users can start using the new mail system immediately.
  • New emails are received in the target messaging system.
  • Old emails are migrated in a single pass.

1.1.2 Cutover migration considerations

You can combine your cutover migration with pre-staging if required. In this case, during the days or weeks leading up to your cutover, you would migrate all emails up to a week or so ago along with calendars and contacts, then on the day of your cutover, you would run a quick delta pass to migrate the remaining items.

2. Security

For more information about security, please refer to this article.

3. Performance

For more information about migration performance, please refer to this article.

4. Mail migration scope

4.1 What can be migrated

When migrating from Zimbra to Office 365, all of the following mail-related items can be migrated:

  • Emails
  • Contacts
  • Calendars
  • Secondary calendars
  • Folders

4.2 Migration limitations

Cloudiway provides a solution that makes the transition trouble-free. Cloudiway’s mail routing platform enables emails to continue to be received and delivered to the correct inboxes during a domain name change. Mail headers are not modified.

The mail routing service is not available by default, so if this functionality interests you, please get in touch for more information and a quote.

4.3 Considerations

Migration takes place between existing mailboxes. This means that mailboxes must exist in the target at the time of migration. Please ensure that all mailboxes to be migrated have had their target mailbox created in the target domain (steps are included in this guide).

4.4 Audience

This guide is aimed at experienced system administrators who are capable of connecting to remote systems and using a variety of administration tools.

Although we provide support for our own products, we do not provide support for third party products such as PowerShell or server administration of Google or Exchange.

If you are concerned you might have any difficulty completing these steps, please consider a solution with our consulting team, contactable via presales@cloudiway.com. This will ensure a fast, costeffective and stress-free implementation.

5. Pre-migration configuration

5.1 Before you start

There are two modes of migration:

  1. Migration with an admin account that has all necessary delegations to all mailboxes.
  2. Self-service migration (when it’s not possible to have a delegated admin account).

Scenario 2 will be used in case Zimbra is a hosted service where the provider cannot give you an account that have permissions to all mailboxes. In this case, you would use the standard self service mode where users migrate themselves by entering their credentials into a form.

How it works

The Cloudiway migration solution is a SaaS platform.
The migration requires the Zimbra server to be accessible from the SaaS platform.

Ports used

Cloudiway migration platform migrates the mails using IMAP.
Contacts and calendars are migrated using the native Zimbra APIs.

Imap ports:
143 : Standard imap port
993 : IMAP over SSL
You will use one of the two ports.

Zimbra admin port: 7071
By default, the Zimbra admin port is 7071. Cloudiway migration platforms needs to connect to the admin platform in order to retrieve information.

Web service ports:
By default, Zimbra web services are accessible through SSL port 443

Firewall rules:
If you want to set up a specific firewall rule, please log a ticket through our Support portal to get our IP-address.


Before you start, you will need to ensure you have the details outlined in the following table.

Name Name Location
Cloudiway login Stores details and provides communication between the systems you already use. https://apps.cloudiway.com
Knowledge base access Our extensive knowledge base is always accessible, with videos, troubleshooting tools, samples and more. https://kb.cloudiway.com
Office 365 account with impersonation privileges Used for impersonation to access mailboxes (read or write). This doesn’t have to be the tenant’s admin account. However, it must be an administrator account if you wish to migrate the permissions. The account must be able to bypass SSO and authenticate using username/password credentials with the format: user@tenant.onmicrosoft.com (with a password set to never expire). We recommend you create a non-federated domain account (on your *.onmicrosoft.com domain) especially for
migration. After all migrations are complete, simply delete this account. We provide steps below to help you set up an account with impersonation privileges if you don’t already have one.

Deactivate MFA On Your Office365 Migration Account (guide: https://kb.cloudiway.com/article/deactivate-mfa-on-your-office365-migration-account/).

5.2 Set up an Office 365 account with impersonation privileges

An account with impersonation privileges can access up to 100 mailboxes concurrently. Therefore, by default, Cloudiway allows you to migrate 100 concurrent users. If you wish to speed up your migration, you should set up additional Office 365 connectors (both source and target) on the Cloudiway platform and associate different accounts with admin access to each one.

Below are the steps to show you how to set up impersonation using the Office 365 Exchange Admin Center. If you don’t already have impersonation set up, please follow the steps below.

  1. Login with your administrator account to the Office 365 portal
  2. Go to the Exchange admin center, then click on permissions and the admin roles
  3. Click on the plus sign (+) to create a new role
  4. Give your group a name and assign it the role of ApplicationImpersonation, then add a user to the group:
  5. Click on the Save button to save your group

6. Use the Cloudiway platform to migrate your mail

6.1 Create your source and target connectors

For Cloudiway to migrate your email, it needs to be able to communicate with both your source and target domains. To do this, Cloudiway uses connectors, which are configured on apps.cloudiway.com. You will need to set up a connector for each source tenant you wish to migrate and each target tenant that mail should be migrated to. Follow the steps below to configure Zimbra and Office 365 connectors.

  1. From your browser, go to https://apps.cloudiway.com and login
    You can choose to manually set up your connectors, or you can use the simpler process of the wizard. The steps below will walk you through the manual process.
  2. Click on Mail Migration on the left, then Sources
  3. Click on the + New option at the bottom of the screen
  4. Click on Zimbra and type a meaningful name in Connector name
  5. Click on the Create button
  6. Click on Mail Migration on the left, then Targets
  7. Click on the + New option at the bottom of the screen
  8. Click on Office 365 and type a meaningful name in Connector name
  9. Click on the Create button
  10. Type your target domain name in Domain
  11. Type your Office 365 account credentials (with administrator and impersonation rights)
  12. The remaining field is for archiving older emails from inboxes (switched off by default):
  13. Leave the Archive mails old than x months option off for now (it’s covered in the next section)

6.2 Create a partial archive from a normal inbox

Creating a partial archive of emails provides a number of benefits. From a migration perspective, the biggest benefit is reduced bandwidth. End-users who access mail via Outlook have their mailbox locally cached (in .ost file format). After a mail migration, Outlook will download all migrated mailboxes the first time users access their mailboxes. Therefore, if many users are likely to access Outlook at around the same time after migration (for example, if you’ve completed a cutover migration one weekend before staff arrive at 9am Monday morning), your bandwidth might slow down due to a glut of downloads.

This can be avoided by partially migrating data to the online archive. For example, you could choose to migrate all items older than 30 days to a mail archive, which would be performed prior to the final cutover. The data will remain online and accessible from each user’s inbox as an In-Place Archive
folder. The most recent 30 days of emails will be migrated and downloaded when each user first logs in, reducing overall bandwidth usage due to smaller mailbox sizes.

Note: you must ensure that In-Place archiving is switched on within your Exchange Admin center (you can bulk-activate using the instructions on TechNet as https://technet.microsoft.com/enus/library/jj984357(v=exchg.150).aspx).

In-Place archives at the source are treated differently to standard mail and are not migrated by default. You can buy a mail archive quota package to perform an archive migration (see section 7.2).

  1. With your target connector selected, click on the Edit button on the action bar at the bottom of the screen
  2. Click on the ON button to activate the Archive mails old than x months option
  3. Enter a number in the field to indicate the minimum age (in months) of mails to be archived
  4. Click on the Save button at the bottom of the screen
    Now, when your migration starts, any emails older than the number of months you specified will be migrated to an In-Place archive. Younger items will be migrated to the target mailbox. The user can continue to use the source mailbox until final cutover, whether it be the following day or in a month’s time.
    During final cutover, all new and remaining emails will be migrated. Note that migrated items are never re-migrated, so the In-Place archive will contain items older than the months you specified from the date of the first migration pass.

6.3 Configure the global settings for migration

Now that you have set up at least one source and target connector, you’re ready to configure your global settings. Using the Cloudiway platform, this is simply a matter of selecting what you want to migrate.

By default, the global migration settings are configured to migrate everything but the Trash folder. You can toggle these and change the date and time settings from the Global Settings option on the Cloudiway platform.

Most of the options are self-explanatory. The Convert Email Address option needs further explanation. When activated, this option rewrites email addresses found in the header and replaces source email addresses with their corresponding target email addresses.

For example, if Bob sends an email to his colleague to Chloe from his source address bob@source.com to chloe@source.com and a week later, after migration, chloe@target.com replies to Bob, the Cloudiway platform has already updated SMTP header in Bob’s original email in her inbox, so her reply will be sent to bob@target.

For migrations where the only email address change is the domain name (such as Bob’s email address above), the Cloudiway platform uses the domain name defined in the target connector to convert source email addresses.

For migrations where both the domain name and the username change (for example, bob@source.com becomes newbob@target.com), the Cloudiway platform already uses a mapping table to link each user. This mapping table is also used by the Convert Email Addresses option in this situation. Therefore, it’s important that all users exist in the mapping table before migration begins (this guide contains instructions).

Note that users in the mapping table do not require a license until you’re ready to migrate them. Therefore, you can assign the free ‘No license’ option to all your users prior to migration. Having a complete mapping table is also required if you plan to use Cloudiway’s free/busy calendar tool in conjunction with mail migration.

The Convert Email Address option is switched on by default (and is best left on). Make sure your user list is up to date to benefit from this functionality.

  1. From the same Mail Migration area of https://apps.cloudiway.com, click on Global Settings
    By default, the global migration settings are configured to migrate everything but the Trash folder. You can toggle these and change the date and time settings in Edit mode. Please refer to the text above these steps for more information on the Convert Email Addresses option.
  2. Click on the Edit button at the bottom of the screen
    The grey buttons will turn blue, indicating you can now edit these to your preferred global migration plan.
  3. Update any settings you wish to alter, remembering that time and dates are set to the UTC time zone
  4. Click on the Save button at the bottom of the screen to update your global settings

6.4 Import or create your users

There are a number of ways to add users that you wish to migrate. These include:

  • CSV file upload;
  • Cloudiway’s Import Users tool; and,
  • creation of single users.

Regardless, each user will need to be assigned a license type — Trial (limited to 100 MB), Education, Standard, Archive, or No License (used for adding users to your mapping table regardless of migration plans).

6.4.1 Option 1: CSV import

If you have a CSV file of all your users, you can upload the file to Cloudiway. The file must have the following fields in the header row:


Note that many browsers limit CSV file uploads to 5000 lines, so files larger than that should be split up and uploaded separately. Data already uploaded will not be overwritten, so you can upload as many files as required.

The BatchName field can be left blank. If required, you can use this field to name different batches so they can be run in a certain order. A sample CSV file is available for download during the steps outlined below.

  1. Ensure you’re still in the Mail Migration area of apps.cloudiway.com and go to User List
  2. Click on Manage on the action bar at the bottom and select Upload CSV
  3. If required, click on Download sample CSV and add your users to the CSV file using the sample headers (FirstName;LastName;SourceEmail;TargetEmail;BatchName)
  4. When you have a complete CSV file with the correct headers, click on the Upload button
  5. Locate your CSV file within your own file system, and double-click on it to select it
  6. Select the appropriate connectors in the Source and Target fields
  7. Select the license type from the License drop-down list
  8. Click on the Upload button.
    If the CSV file format is not correct, you will see an error message on your screen:
  9. If you see any error messages, check your CSV file to ensure it has five columns with a separator between each and try uploading again
  10. Once the CSV file format is correct, you will see a confirmation message at the top of your screen:
  11. Check your email. When you have received confirmation that the upload has been completed, you can refresh the Cloudiway platform to display your imported users.

6.4.2 Option 2: Import Users tool

Cloudiway’s Import Users tool helps you to retrieve users from your source tenant. The functionality works via Identity Access Management. The tool requires you to specify any transformation rules you wish to apply. It will then add new users in the Mail Migration User List view within the Cloudiway platform.

This is an advanced tool that is best used in partnership with Cloudiway consultants. If you are interested in using this option, please get in touch with your Cloudiway contact.

6.4.3 Option 3: Single user creation details

Many of our first-time customers create a single user for testing purposes. This provides a means of watching the migration process without affecting all users. Single users can also be created for migrations affecting just a few users.

  1. Go to the User List of the Mail Migration menu
  2. Click on Manage on the action bar at the bottom and select Create Single to display the following screen:
  3. Fill in all details for a new user
  4. Click on the Create button
    The new user will be added to the Mail Migration / User List screen:
  5. Repeat steps 1 to 4 for any more users you’d like to create

6.5 Activate and monitor your migration

Now that you have performed all the pre-migration steps within your tenants and within Cloudiway, you’re ready to migrate. We recommend you run a test migration on a single user first to check that your configuration produces the outcome you expect.

To start your migration, select the users or batch you wish to migrate and click on the Start button. Your batch will be scheduled and will begin as soon as resources are available. By default, a hundred migrations can be run concurrently per connector.

Don’t forget that Cloudiway migration platform supports delta passes and that migrations are therefore incremental; every time you restart the migration of a mailbox, only items that haven’t already been copied to the target will be migrated. The platform therefore does not duplicate items in the target.

6.6 Migrate permissions globally

You can globally migrate permissions for mailboxes through the Cloudiway platform.

NOTE: Once you start the process of setting permissions, it cannot be stopped.

  1. From the same Mail Migration area of https://apps.cloudiway.com, click on Global Actions
  2. Click on the Migrate Permissions option on the screen to display the following dialog box:
  3. Click on the Set button to trigger the Cloudiway platform into setting permissions on all mailboxes

7. Troubleshooting

Cloudiway provides an extensive knowledge base with many resources, including common error messages, video guides and downloads.

Please visit the entire knowledge base here (where you can search for keywords or read through topics): https://kb.cloudiway.com/

The knowledge base also contains information on how you can ask for further support, should you require it.

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