Gmail won't work on the launch firmware, so it is entirely possible you need to update the printer.
The error you get could be that the printer firmware you have doesn't support SHA-2 (firmware update will resolve) or that the login info or rest of the setups is wrong.
I find SSL/TLS and port 587 works, but others use SSL/TLS on 465. STARTTLS often has issues.
Very important that the from address in both locations and the login name are identical.
So Properties>Connectivity>Setup>SMTP(Email)>Edit>Device Eimail Address
And Properties>Connectivity>Setup>SMTP(Email)>Edit>SMTP Authentication (Make sure both are on System and using the same as the from address.
Then Properties>Services>Email>Setup>From Field (This one often has issues updating from the other location and vice versa, this applies to all Connectkey devices and firmware levels straight up to the current