Our printer still works, only thing we have recently had to alter is because Google have pushed up there security we have had to enable 2FA on the Google account and create a App password which the Printer uses instead of the normal login password. It is the same setup we are using on a newer Xerox printer also.
My IT department has also tried this similar thing that you mentioned and still nothing has been resolved. We had a Xerox rep even come out and replace the board on the machine because they thought that was the issue. They also mentioned that the scan to email may not get corrected since the machine is to old.
I had the same issue with my new email hosting provider. Cost me two days to
figure it out. Even though I was using port 587 for SSL/TLS in Apple Mail
for my smtp server at ionos. It didn't work on the machine.
I switched to port 465 instead and that seams to work with my email hosting
provider in combination with SSL/TLS.
found the problem to be the Gmail account, the computer is in a remote location from our main office and was Google was blocking the other site's IP address, soon as I logged into the account from the other site it prompted me make sure that it was signing in from this site using the recovery email address and the the scan to email functional was restored.
SSL settings: Use StartTSL if available
Email Settings: port 587, SMTP server smtp.gmail.com, I used authenication with the gmail address and password afterwards.
Thanks all that helped
016-764 means it connected but then got an invalid response from the mail server (Printer gets confused and just stops)
So if you get that on the latest firmware, then Google likely changed something on their end that the printer can't do.
Your best bet is to use something like SMTP2Go assuming you have already followed the plethora of gmail topics posted here already