Site Admins can update email addresses for many users at once using the Bulk Email Update Tool.
To use this tool, you'll follow the instructions on the page to download a .csv of all users in your system, add new emails to the spreadsheet, and upload it. Once the migration is complete, the new addresses will be added as Secondary emails to all affected users.
Run the email migration tool
Navigate to Configure > Email Settings > Email Migration tool.
Follow the instructions on the screen to move through the migration process. When you're ready, click Start Migration.
When a migration is complete, an email will be sent to the submitter containing any email addresses that could not be changed.