You can also send email from your terminal using a traditional mail agent like mutt, which also installs via homebrew, but doesn’t require a proprietary API key to send email. Mutt will happily send email as your Gmail user. Mutt can also read email, so if you really live in the terminal it can do it all.
https://www.makeuseof.com/install-configure-mutt-with-gmail-...
neomutt even has a litany of cool new features like TLS SNI, threading and encrypt-to-self.