Migrating gmail from one G suite account to another
See also
References

Migrating gmail from one G suite account to another

If you have Essentials edition Google Workspace edition (aka Gsuite), you can only migrate contacts. You can't migrate email or calendar data.¹⁾

The data migration service does not remove data from the source mailbox, nor does it remove the original source mailbox. All eligible data is copied during a migration, not moved/deleted, and the data in your source mailbox remains after a migration.²⁾

You can’t migrate messages bigger than 25 MB.³⁾

Migrating large mail accounts might take a lot of time. For example migration of cca. 1.5GB mail account took almost 3 days!!! But this will depend on how many attachments there are in the account, number of emails etc.

NOTES:

Enable IMAP on both the source and destination account
“Folder size limits” in Gmail Settings must be set to “Do not limit the number of messages in an IMAP folder (default)”. This is the default.
when migrating from multiple domains you must add MX records for them
on the migration assistant screen, when you are done with emails from one domain exit the Migration Assistant (More > Exit migration) then start the migration again for the users with new domains. If you don't do this you'll get an error “Failed estimating mailbox size”.
if you are transferring the same domain, make a temporary domain with mx records on the source account and move user's email to this domain. Then remove the domain from source account and add it to the destination account
domain can only be removed once the user's email and email aliases are removed (check each user > User information > Alternate email addresses (email alias)). Remove the domain you are transferring from here.

Set up the data migration service

Sign in to your Google Admin console.
Sign in using an account with super administrator privileges (not your current account user@gmail.com).
From the Admin console Home page, go to Data migration.
Click Set Data Migration Up.
Under Migration Source, select Google Workspace.
Click Start.
Under Migration Start Date, accept the option that appears or choose a start date for your migration.
Under Migration Options, accept the options that appear or choose to exclude some data.
Click Select Users.

Migrate email from another Google Workspace account

Perform the following steps on your target Google Workspace domain (the account you're migrating to).

Migrate email for a single user

Click Add user.
In the Source Email field, enter the user's legacy Google Workspace email address.
In the Google Workspace Email field, start entering the user's new Google Workspace email address and choose from the list of suggested users.
In the Password field, enter the user's password for their legacy email account.
Click Start.
(Optional) To migrate another user's email, repeat these steps.

Migrate email for multiple users

Click Bulk upload with csv.
Click Attach File to upload the migration CSV file containing the legacy email addresses and the new Google Workspace email addresses.
For details on how to format the file, see references below.
Click Upload and Start Migration.
If there are errors in your file, choose an option:
To update the file, click Cancel. Then, upload the updated file.
To ignore the incorrect mappings, check the Ignore errors box.

Tip: To exit a completed migration, click Moreand thenExit migration.

References

¹⁾

https://support.google.com/a/answer/9476255

²⁾ , ³⁾

https://support.google.com/a/answer/7032598

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