1. How to migrate mailboxes from IMAP to Microsoft 365

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Office 365 account with impersonation privilegesUsed 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: (with a password set to never expire).We recommend you create a non-federated domain account (on your * 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.
Mail Migration Global Settings
1. Ensure you’re still in the Mails Migration area of and go to User List 
Mails migration User Listing
2. Click on MANAGE and select Import

5.4.6. Create your shared mailboxes

Cloudiway provides a tool to provision and migrates shared mailboxes in a separate menu. In the Mail Migration section of the tools, you will see a Shared Mailboxes option. This tool can be used to discover your shared mailboxes and provision them to the target tenant so you don’t have to do it manually.

More details on how to use this feature can be found here:

5.5. Mapping Table

During the migration, Cloudiway uses a mapping table to perform the conversion of email addresses in email headers, calendar items, and mailbox permissions.

Important: the mapping table must be exhaustive, any missing email address will not be converted, and would end up with loss of mailbox permissions, unrepayable emails and broken calendar items. Cloudiway automatically populates this mapping table when source mailboxes are discovered by Get List functionality explained below. However, make sure if the mapping table was populated automatically that you are not missing any email address.

6. Use the Cloudiway platform to migrate your mailboxes

6.1. Create Your Connectors

For Cloudiway to migrate your Mailboxes, it needs to be able to communicate with both your source Exchange On Premises and target Microsoft 365 tenant. To do this, Cloudiway uses connectors. You will need to set up a connector for the Exchange On Premises you wish to migrate and target tenant that mail should be migrated to. Follow the steps from this page to configure your connectors.

Mail Migration Global Settings

Most of the options are self-explanatory.

The Convert Email Address option needs further explanation. The Convert Email Address option is switched on by default (and is best left on). When activated, this option rewrites email addresses found in the email headers, calendar items and mailbox permissions and replaces source email addresses with their corresponding target email addresses in the mapping table. Therefore, it’s important that all users exist in the mapping table before migration begins.

Archive Mails Older Than is to migrate the emails older than specified date and time in the past to the target archive mailbox and Migrate Everything to Archives is to migrate all the emails to the target archive mailbox. See the 7.3.2. Migration to archives section for further information.

Click on the Save button at the bottom of the screen to update your global settings.

6.3. Import or create your users into Cloudiway platform

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

  1. CSV file import.
  2. Cloudiway’s mailbox discover tool (Get List).
  3. Create a single user.

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).

Note that importing users into Cloudiway won’t create the user mailboxes in the target tenant. See 5.6. Create your user mailboxes

6.3.1. Option 1: CSV file 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:


Archive Mails
Mails migration UserList Import
Zimbra to Microsoft 365 migration
Mails migration Create Users

For more information regarding the different fields, check out this article. Repeat the process 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.

Cloudiway is an incremental migration platform that supports delta passes. Every time you restart the migration of a mailbox, only items that haven’t already been copied to the target will be migrated and for those already migrated items that have been modified in the source will be updated in the target. The platform, therefore, does not duplicate items in the target, just updates them.

The migration strategy usually consists of at least 2 migration passes, one before the cutover and another pass after the cutover:

  • 1st migration pass: which migrates the majority of the mailbox. Select mailboxes, click on MIGRATION, then the Start button. Explained below in more detail.
  • Cutover: You have to manually remove the domain from the source tenant, attach it to the target tenant and change the MX record in your DNS server. This is not automated by Cloudiway.
  • 2nd migration pass, delta pass: which migrates what hasn’t been migrated and updates modified items. Select mailboxes, click on MIGRATION, then the Start button. Explained below in more detail.
  • 3rd migration pass, delta pass: 24 hours after cutover you can submit an additional delta pass to make sure no residual email is left behind due to DNS propagation delays. Select mailboxes, click on MIGRATION, then the Start button. Explained below in more detail.

You can submit as many migration passes as you want for 3 months and until consuming the amount of GBs allowed by the assigned licenses but usually, you only need one before the cutover and another after the cutover. Find out more about the delta migration passes:

What a migration pass takes to complete depends on a lot of factors. Find out more about the migration performance:

If you have moved the source domain and need to perform one more delta pass, the Switch Domain global action will need to be used:

You can create user batches from the Batches tab to easily group subset of mailboxes. Click on the + icon and enter a batch name:

Add users to batch

After creating the different batch, under Users tab, select the users you want to assign to a specific batch, click on BATCH button and Add to Batch:

Add to batch

To start your migration, select the users or batch you wish to migrate.

  • For users, under Users tab, select all the users you want to submit and click on MIGRATION, then the Start button.
User list
  • For user batch, under Batches tab, select the user batch you want to submit and click on MIGRATION, then the Start button.

Your migrations will be scheduled and will begin as soon as cloud resources are available.

NOTE: When migrating by user batches during a long period of time you may want to enable email forwarders.

For more information, please see this article:

7. Other migration options

7.1. Mailbox permissions migration

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

Migration of permission isn’t performed during the migration of the mailboxes but through a dedicated job.

The migration of the permissions will migrate permissions on the mailboxes, on the primary and secondary calendars.

WarningIf permissions were applied to mail-enabled security group, the mail enable security group must exist at the destination for the permission to be applied correctly.

Click on User List, select the users, go to MIGRATION, then click on Migrate Permissions

Migration Permission

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

7.2. Migrate to archives

The IMAP mailboxes can be migrated to the Microsoft 365 online mailboxes, to the Microsoft 365 archives, or to a mix of both.

During the migration, a single mailbox can be split into the online mailbox and archive.

Note: to migrate content to archives, In-Place archiving must be enabled for the user, learn more:

In the Cloudiway platform, you can migrate either only old emails or all the emails to the target archive mailbox. So, 2 options:

  • From the Global Settings section, Archive Mails Older Than is to migrate the emails older than specified date and time in the past to the target archive mailbox. Keep Migrate Everything to Archives disabled.
Archive Mails

In this example emails older than April 7 2020 will be migrated to the archive mailbox:


Click on the Save button, when your migration starts, any emails older than the date you specified will be migrated to an In-Place archive. More recent items will be migrated to the target mailbox.

  • From the Global Settings section, Migrate Everything to Archives is to migrate all the emails to the target archive mailbox. In the Mail Global Settings, enable Migrate Everything to Archives and all emails will be migrated to the target archive mailbox:
Archive mails

Click on the Save button, when your migration starts, all emails will be migrated to an In-Place archive.