When sending Mime-Email the mandatory header file MIME-Version is not always set.

Example to reproduce the error:

  $mail = new Zend_Mail();
  $mail->setFrom('xxxx@xxxx.de', 'Tester');
  $mail->addTo('xxxx@xxxx.de');
  $mail->setSubject('testmail');
  $mail->setBodyText('Test Test äöü ','ISO-8859-1','quoted-printable');
  $transp = new Zend_Mail_Transport_Smtp('xxxx.xxx.de');
  $mail->send($transp);

Remarks: In Body text there are german umlauts (Real-names are replaced by xx)

When looking at the generated Mail, it is lacking the header field:

MIME-Version: 1.0

The error could be corrected in File Zend/Mail/Transport/Abstract.php in function _getHeaders($boundary) with adding the following code:

else $this->_headers['MIME-Version'] = array('1.0');

just befor the return $this->_headers; at the end of the function.