Mischief managed. Just POST the message to https://www.googleapis.com/upload/gmail/v1/users/me/messages/send?uploadType=media with these headers...
Authorization: Bearer <access token>
Content-Length: <message size>
... and you're good to go.
@david I've just started using Mutt again, too. Also with Gmail at work. Very exciting indeed.
arktos.social is a private Mastodon instance. Contact the administrator to request an account.