By default, a single SMTP transport creates a single connection and re-uses it for the lifetime of the script execution. You may send multiple e-mails through this SMTP connection. A RSET command is issued before each delivery to ensure the correct SMTP handshake is followed.

Optionally, you can also define a default From email address and name, as well as a default reply-to header. This can be done through the static methods setDefaultFrom() and setDefaultReplyTo(). These defaults will be used when you don't specify a From/Reply-to Address or -Name until the defaults are reset (cleared). Resetting the defaults can be done through the use of the clearDefaultFrom() and clearDefaultReplyTo.

If you wish to have a separate connection for each mail delivery, you will need to create and destroy your transport before and after each send() method is called. Or alternatively, you can manipulate the connection between each delivery by accessing the transport's protocol object.