What RFC defines the Envelope Mail From

Which of the following SMTP Commands defines the Envelope Mail From

Which of the following headers defines that a Mail is an Auto Reply

An Authentication wherein it checks if the Sender's IP Address is permitted to send an email for a that particular Domain

An Authentication wherein it checks the Envelope From Alignment

A command used to check if the port is open

Is there a way to check if a recipient or sender is blocked by the Backend Team on HES using the support account?

Protocol used when sending Mails

Which of the following is the Envelope Mail From when reading the Headers