I don't use Gmail as my forwarder, so these are only guesses:
The host should probably be smtp.gmail.com, per
https://support.google.com/a/answer/176600?hl=en''
It is unclear to me why you have a "label" record in your <secrets> table, and why you have "gmail" as your userid in the second record.. See the table(5) man page for the proper format of a credentials table, which has two entries per record: userid, then password.