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You can view and fix email delivery failure errors that occur when a new user account is created, or any of the following changes are made to an existing user account:
- Added an account
- Reset password
- Password expiration notification
- Password expired
- Changed password confirmation
- Forgot username
A red flag appears at the top of a page when an email delivery failure occurs.
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Step-by-Step
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Click the flag to reveal a list, and select Email Delivery Failures.
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Alternatively, from Setup, select Users. To find users with email failures, select Only Users With Email Failures under Toggle secondary filters.
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Expand title View details... 
2.
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Review the user accounts and make updates.
3. Click Save.
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