Windows 10 has no bearing unless the email server (SMTP) is your PC.
The only reasonable cause would be that the SMTP server you use, just got an update of some sort, and now it is giving a response back to the printer when it sends an email it is not capable of understanding, so it displays a failed message, and assumes it did.
Easiest fix is to simply disable the confirmation report.
Next up would be a firmware update
Then, if that failed, call Xerox to report it if you want them to spar (fix) it.
Hello, my Xerox Phaser 3635MFP is spitting out an email confirmation report showing " job status: failed " although the email did go out. since i get a copy of all outgoing emails in my inbox i can see them going to their respective destination. i even performed another test this morning and all recepients got the test message including myself but the machine still printed out the report showing 'job status: failed'. any ideas? FYI..running Windows 10.