Assuming that you have GoogleApps-enabled domain and already established Office 365 tenant domain – target for the migration of user accounts and their mailboxes.
Here are some tips and procedures for efficient migration project:
Microsoft’s official guide “Migrate Google Apps mailboxes to Office 365” in section “Create a list of Gmail mailboxes to migrate” says:
“When you create the migration file, you need to know the password of each Gmail mailbox that you want to migrate. We’re assuming you don’t know the user passwords, so you’ll probably need to assign temporary passwords (by resetting the passwords) to all mailboxes during the migration. You must be an administrator in Google apps to reset passwords.”
Mass-management of gmail users’ passwords means temporary mailboxes unavailability for end-users under the migration scope (specified migration group or all users in the migrated GoogleApps domain) because you will need to reset the password to something known to you.
Next steps described as:
2. After you’re signed in, choose Users.
3. Hover over each name to identify each user’s email address. Write down the address.
4. To reset each user’s password, hover over each user name and choose Reset Password. Reset the password and write the new password down next to the related user name.
– which is totally irrelevant for you in case you are going to migrate hundreds or thousands of mailboxes. Instead – you will need three copies of exported Gmail users lists: – 1) To create user accounts in Office365, 2) to reset gmail users’ passwords, and 3) for the migration job.
I. Bulk export/import of user accounts
To export Gmail users list:
- Sign in to Google admin console using your administrator username and password.
- Choose Users, make sure you see the necessary scope (Filter) of users
- In the top-right corner use tool, select “Download users”:
- Select “All users” or a filtered scope, make three copies of an obtained CSV file.
Tip: Make sure you edit the CSV file in Unicode (UTF8) format if you migrate users with national symbols (like å ,ø, æ etc) in names!
Proceed with the recommended guide to import user accounts to Office365, assign licenses to create mailboxes and email addresses.
Although newly created Exchange Online mailboxes are empty – they are ready for use if you decided to re-route mailflow (with MX DNS records) from Gmail to Office 365 in this stage. Nothing prevents you from making the mail services available for users in the first stage, and transfer mailbox contents at the next.
Tip: It can take up to 72 hours for the email systems of your customers and partners to recognize the changed MX record.
II. Bulk reset gmail users’ passwords
Another copy of your downloaded users list can be used for mass-resetting gmail passwords for the data migration procedure.
To migrate mailbox data you ought to have their passwords known. Gmail exported file of course does not yield passwords, so you need to edit the CSV and re-import it back to Google Apps with known passwords. There can be a single temporary “migration password” for all gmail accounts, for security reasons you must not disclose this temporary password to end users and must destroy the passwords-import file after use.
- This is CSV you get from Gmail export
- and this is how you edit the CSV to import with passwords:
- Then, in the Google admin console hover tool to reach “Add multiple users” menu, where you import the CSV file with passwords:
III. Mailboxes migration
Finally you have the user accounts in target Office 365, as well as known-passwords-accounts in the source Gmail. Now you will need the 3rd copy of your users list to form the migration job.
Here is how your mailbox migration list should look like:
where Column A is the name of the Office 365 mailbox, Column B is the Gmail mailbox, and Column C is the password for the Gmail mailbox.
You are good to go with the rest of Microsoft migration guide.