Features Install. The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols, such. The mail server responds with 235 Authentication successful. Getting this far indicates that your connection to smtp.sendgrid.net over the chosen port is open and that your API key is valid. Next, add the email that you're sending from: mail from:<<SENDER_EMAIL>. The mail server responds with 250 Sender address. Incoming and Outgoing…