Hi,
You want to create Email provider?
About your read-only problem, our default email provider cannot be edited. That is the place you see this, correct?
To create Email provider based on your Gmail, you should set the provider protocol to SMTP and follow the documentation below.
"Gmail SMTP server" column.
https://support.google.com/a/answer/176600?hl=en
When you test your Connector, you might get error because Google may think the SMTP request came from un-trusted source.
In that case you have to login to the Google account from browser and let Google know that you are aware of this transaction.
Best regards,
Taka