(where ... == the rest of the line)

open (SENDMAIL ...)        ==>  $smtp=new Net::SMTP("localhost");
print SENDMAIL "HELO ..."  ==>  (implicit)
print SENDMAIL "MAIL ..."  ==>  $smtp->mail(...);
print SENDMAIL "RCPT ..."  ==>  $smtp->to(...);
print SENDMAIL "DATA"      ==>  $smtp->data();
print SENDMAIL "..."       ==>  $smtp->datasend(stuff);
print SENDMAIL "."         ==>  $smtp->dataend();
print SENDMAIL "QUIT"      ==>  $smtp->quit();