Sandboxes have separate email deliverability settings from production. By default, sandbox email deliverability can be set to 'No Access' to prevent accidental emails to real customers during testing. This error occurs when a user tries to log in but the system cannot send the required verification or password reset email.
Users are directed to a page with the following error message:
"Email Not Sent.
The email could not be sent due to an error with the email delivery system.
Click here to return to the previous page"
To gain access to the Sandbox, email deliverability must be set to "System Email" or "All Email." This change must be made by Salesforce Support.
If you've confirmed the email deliverability is set to "No Access" and still need assistance, please have a System Administrator create an activation request with Support.
000393360

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