If you migrated to Google Workspace's email service, note that your old mailboxes created in hPanel will no longer work! No worries as you will be able to transfer your old emails to Gmail, all you will need is to access your webmail:
Once there, click on the top right Settings selection. Click on the Accounts and Import tab, and in the second section, select Import mail and contacts. Afterwards, you will only need to follow the steps on the screen and select the Start import option 😊