When Instantiating a Zend_Mime Object, a MIME
boundary is stored that is used for all subsequent non-static method calls on that
object. If the constructor is called with a string parameter, this value
is used as a MIME boundary. If not, a random MIME
boundary is generated during construction time.
A Zend_Mime object has the following Methods:
boundary(): Returns the MIME boundary string.boundaryLine(): Returns the complete MIME boundary line.mimeEnd(): Returns the complete MIME end boundary line.