"Send Test Email" error 550: mailbox unavailable
I am using WebCenter Content Server 11.1.1.8.
During development, I used my own email as the Admin email (set in Admin Server - Internet Configuration or in the Administration Console under Summary of eMail Sessions). I recently changed it to our official Admin email and can no longer send emails through WebCenter. Both the Administration - Admin Server - Internet Configuration and Administration Console say the correct email. In the User's App, SysAdmin also has the correct Admin email.
But when I attempt to use Send Test Email, I get this message:
Unable to send email. Could not send mail message from my_name@my_company.com with subject line: Test email from Content Server. Mail server responded with error message: 550 Requested action not taken: mailbox unavailable