If your device or application does not support SSL, connect to aspmx.l.google.com on port 25.
It’s amazing what happens when you do some more research. Turns out I don’t need the Pi to act as a mail bridge between my scanner and the outside world. Google already has that covered, although I wonder when they set this up? It wasn’t like this a few years back when I did have to set up a mail server to act as an in between!
Now to find something else to use the Pi for!