Hello wo1de,
This could be an issue with SSL/TLS on SMTP. I found a previous post related to this error here:
https://forum.support.xerox.com/t5/Copying-Faxing-Scanning/CM405df-scan-to-email-016-764/m-p/182607
Hello!
Sometimes i got interesting error code in my printer.
He cant send me scanned documents by mail and writing the error code 016-764.
How i can fix it? What should i need to do?