First, follow the Twilio Setup guide for creating a Twilio account and setting up environment variables with the proper credentials.
Then, initialize the Twilio Email Client.
mailClient := NewTwilioEmailSendClient(os.Getenv("TWILIO_API_KEY"), os.Getenv("TWILIO_API_SECRET"))
// or
mailClient := NewTwilioEmailSendClient(os.Getenv("TWILIO_ACCOUNT_SID"), os.Getenv("TWILIO_AUTH_TOKEN"))
This sets the client to use Twilio Auth and the Twilio Email API.