Mass Update Salesforce Usernames While Avoiding Email Notifications

Workaround 1: Temporarily Disable Email Deliverability

It is possible to temporarily disable all email for the entire Salesforce organization while performing the username updates. This prevents the username-change notification emails from being sent.
In Salesforce Classic: Navigate to Setup > Administer > Email Administration > Deliverability.
In Lightning Experience: Navigate to Setup > Email > Deliverability.
Change the Access Level to "No Access" and save.
After making this change, email notifications generated when usernames are changed will not be sent.
Important: Be sure to revert the Access Level to its original setting (typically "All Email") after completing all username updates. Setting email to "No Access" prevents all emails from being sent, including system emails and password reset emails.

Workaround 2: Deactivate, Update, and Reactivate Users

As an alternative workaround, for each user:

1. Deactivate the user (without removing them from any teams).
2. Change the Username while the user is deactivated.
3. Reactivate the user.

This prevents the username-change notification email from being generated.
Note: If Workflow rules or other automation triggers are configured to fire upon user activation in your org, deactivate those automations first. Otherwise, those automated emails will fire when the user is reactivated.



See also
Configure Deliverability Settings for Emails Sent from Salesforce
Guidelines for Configuring Deliverability Settings for Emails Sent from Salesforce
Mass update email addresses and usernames