Just like anything else the 9303 has to log into the email server, so when you changed your passwords you blocked access from the device since you stated nothing has been changed on the printer.
Take the IPv4 address found on the machine status screen and put it in the address bar of your web browser (Don't use Chrome though)
This will load the printers web interface.
Go to Properties > Connectivity > Setup and select the Edit for the SMTP (Email) option.
Then select the SMTP Authentication option and update the passwords for the printers email address.
