The Sender line is being added by the Mail Tranport Agent (MTA).
The concepts of Sender and From are separate. If you do not specify a Sender, the MTA (typically sendmail on a Unix system) may add a Sender field if the mail does not appear to be coming from the user specified in the From field. Read Internet RFC822 for definitions and purposes of From and Sender.
To add a Sender line to your PHP mail formatting, or any other line, simply add it to the headers argument of the mail() function.
mail($recipient,$subject, $message,
"From: $name <$email>\nSender: A PHP automated process from $name <$email>");