If pipelining is enabled on your server, commands are stored internally in the client as they are issued. Pipelining may then be enabled if the server supports it. If not, the way the network works does not change. The ehlo callback indicates whether pipelining is supported. For this method's callback mapping, see SMTP Callback Mapping .
Some methods continue to add to the pipelining list.
Calling any other method causes the methods on the pipelining list to begin executing. For example, you could call mailFrom , followed by one or more calls to rcptTo . These methods are added to the pipelining list and are not executed. If you then call another method, such as noop , the commands are sent to the server. It sends the MAIL FROM SMTP protocol command.