Salesforce automatically sends notification emails when usernames change. You cannot disable this directly, but you can use these workarounds to prevent users from receiving the notification email upon a username change.
When changing a user's EMAIL or USERNAME, Salesforce sends an email notification to the owner about this change. However, you can disable this notification only for EMAILS but not for USERNAMES. It is possible to suppress the email notification upon changing a user's EMAIL address, but not upon the USERNAME change. Refer to Disable Email Change Verification for information on the process to suppress notifications on EMAIL address changes.
All Editions
Use one of the available workarounds below
Review the workaround options below to determine the best approach for your organization before making any username changes.
There is a workaround so that users will still not receive the email notification upon username change. Please review this documentation for your reference: How to Mass Update Usernames without Sending Email Notifications
Another workaround is to deactivate the user (but do not remove them from any teams). After deactivating, change the Username and then reactivate the user. This will forego the notification email that the Username has been changed.
Important: If there are other emails via Workflows or other triggers that are set to fire upon activation of a User in your org, those will need to be deactivated first. Otherwise, those emails will fire upon activation of the user.
An idea for this feature has been created. Please review Disable email verification when changing a user's username.
Click the Upvote button to support this idea. You may also encourage your colleagues to vote and promote the idea. Once this idea gathers enough votes, it may be considered in a future release.
If you need to disable the email notification for an email change, please review Disable Email Change Verification.
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