Index: library/Zend/Mail.php
===================================================================
--- library/Zend/Mail.php	(revision 10937)
+++ library/Zend/Mail.php	(working copy)
@@ -115,6 +115,12 @@
     protected $_date = null;
 
     /**
+     * Message-ID: header
+     * @var string
+     */
+    protected $_messageId = null;
+
+    /**
      * text/plain MIME part
      * @var false|Zend_Mime_Part
      */
@@ -461,6 +467,28 @@
     }
 
     /**
+     * Helper function for creating a RFC 2822 compliant Message-ID header
+     *
+     * Inspired by MailMan implementation at
+     * http://mail.python.org/pipermail/mailman-developers/2002-April/011407.html
+     *
+     * Sample Message-ID:
+     *   <20020201195627.33539.96671@host1.mydomain.com>
+     */
+    protected function _createMessageId()
+    {
+        $utcDate = gmstrftime('%Y%m%d%H%M%S');
+        $pid = getmypid();
+        $rand = mt_rand(0,100000);
+        $hostName = php_uname('n');
+        if (isset($_SERVER["SERVER_NAME"])) {
+            $hostName = $_SERVER["SERVER_NAME"];
+        }
+        $messageId = vsprintf('<%s.%s.%s@%s>', array($utcDate, $pid, $rand, $hostName)); 
+        return $messageId;
+    }
+
+    /**
      * Adds To-header and recipient
      *
      * @param  string $email
@@ -660,6 +688,41 @@
     }
 
     /**
+     * Sets Message-ID header
+     *     
+     * @param  string    $id
+     * @return Zend_Mail Provides fluent interface
+     */
+    public function setMessageId($id = null)
+    {
+        if ($this->_messageId === null ) {
+            if ($id === null) {
+                $this->_messageId = $this->_createMessageId();
+            } else {
+                $this->_messageId = $id;
+            }
+            $this->_storeHeader('Message-Id', $this->_messageId);
+        } else {
+            /**
+             * @see Zend_Mail_Exception
+             */
+            require_once 'Zend/Mail/Exception.php';
+            throw new Zend_Mail_Exception('Message-ID Header set twice');
+        }
+        return $this;
+    }
+
+    /**
+     * Returns the Message-ID of the email
+     *
+     * @return string
+     */
+    public function getMessageId()
+    {
+        return $this->_messageId;
+    }
+
+    /**
      * Add a custom header to the message
      *
      * @param  string              $name
@@ -718,6 +781,10 @@
             $this->setDate();
         }
 
+        if (is_null($this->_messageId)) {
+            $this->setMessageId();
+        }
+
         $transport->send($this);
 
         return $this;