diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index 6ff3efa..f8772c6 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -150,13 +150,6 @@
 	public $charset		= 'UTF-8';
 
 	/**
-	 * Multipart message
-	 *
-	 * @var	string	'mixed' (in the body) or 'related' (separate)
-	 */
-	public $multipart	= 'mixed';		// "mixed" (in the body) or "related" (separate)
-
-	/**
 	 * Alternative message (for HTML messages only)
 	 *
 	 * @var	string
@@ -261,20 +254,6 @@
 	protected $_finalbody		= '';
 
 	/**
-	 * multipart/alternative boundary
-	 *
-	 * @var	string
-	 */
-	protected $_alt_boundary	= '';
-
-	/**
-	 * Attachment boundary
-	 *
-	 * @var	string
-	 */
-	protected $_atc_boundary	= '';
-
-	/**
 	 * Final headers to send
 	 *
 	 * @var	string
@@ -743,7 +722,8 @@
 			'name'		=> array($file, $newname),
 			'disposition'	=> empty($disposition) ? 'attachment' : $disposition,  // Can also be 'inline'  Not sure if it matters
 			'type'		=> $mime,
-			'content'	=> chunk_split(base64_encode($file_content))
+			'content'	=> chunk_split(base64_encode($file_content)),
+			'multipart'	=> 'mixed'
 		);
 
 		return $this;
@@ -761,15 +741,11 @@
 	 */
 	public function attachment_cid($filename)
 	{
-		if ($this->multipart !== 'related')
-		{
-			$this->multipart = 'related'; // Thunderbird need this for inline images
-		}
-
 		for ($i = 0, $c = count($this->_attachments); $i < $c; $i++)
 		{
 			if ($this->_attachments[$i]['name'][0] === $filename)
 			{
+				$this->_attachments[$i]['multipart'] = 'related';
 				$this->_attachments[$i]['cid'] = uniqid(basename($this->_attachments[$i]['name'][0]).'@');
 				return $this->_attachments[$i]['cid'];
 			}
@@ -914,19 +890,6 @@
 	// --------------------------------------------------------------------
 
 	/**
-	 * Set Message Boundary
-	 *
-	 * @return	void
-	 */
-	protected function _set_boundaries()
-	{
-		$this->_alt_boundary = 'B_ALT_'.uniqid(''); // multipart/alternative
-		$this->_atc_boundary = 'B_ATC_'.uniqid(''); // attachment boundary
-	}
-
-	// --------------------------------------------------------------------
-
-	/**
 	 * Get the Message ID
 	 *
 	 * @return	string
@@ -993,9 +956,9 @@
 	{
 		if ($this->mailtype === 'html')
 		{
-			return (count($this->_attachments) === 0) ? 'html' : 'html-attach';
+			return empty($this->_attachments) ? 'html' : 'html-attach';
 		}
-		elseif	($this->mailtype === 'text' && count($this->_attachments) > 0)
+		elseif	($this->mailtype === 'text' && ! empty($this->_attachments))
 		{
 			return 'plain-attach';
 		}
@@ -1301,7 +1264,6 @@
 			$this->_body = $this->word_wrap($this->_body);
 		}
 
-		$this->_set_boundaries();
 		$this->_write_headers();
 
 		$hdr = ($this->_get_protocol() === 'mail') ? $this->newline : '';
@@ -1309,7 +1271,7 @@
 
 		switch ($this->_get_content_type())
 		{
-			case 'plain' :
+			case 'plain':
 
 				$hdr .= 'Content-Type: text/plain; charset='.$this->charset.$this->newline
 					.'Content-Transfer-Encoding: '.$this->_get_encoding();
@@ -1326,7 +1288,7 @@
 
 				return;
 
-			case 'html' :
+			case 'html':
 
 				if ($this->send_multipart === FALSE)
 				{
@@ -1335,14 +1297,16 @@
 				}
 				else
 				{
-					$hdr .= 'Content-Type: multipart/alternative; boundary="'.$this->_alt_boundary.'"';
+					$boundary = uniqid('B_ALT_');
+					$hdr .= 'Content-Type: multipart/alternative; boundary="'.$boundary.'"';
 
 					$body .= $this->_get_mime_message().$this->newline.$this->newline
-						.'--'.$this->_alt_boundary.$this->newline
+						.'--'.$boundary.$this->newline
 
 						.'Content-Type: text/plain; charset='.$this->charset.$this->newline
 						.'Content-Transfer-Encoding: '.$this->_get_encoding().$this->newline.$this->newline
-						.$this->_get_alt_message().$this->newline.$this->newline.'--'.$this->_alt_boundary.$this->newline
+						.$this->_get_alt_message().$this->newline.$this->newline
+						.'--'.$boundary.$this->newline
 
 						.'Content-Type: text/html; charset='.$this->charset.$this->newline
 						.'Content-Transfer-Encoding: quoted-printable'.$this->newline.$this->newline;
@@ -1361,14 +1325,15 @@
 
 				if ($this->send_multipart !== FALSE)
 				{
-					$this->_finalbody .= '--'.$this->_alt_boundary.'--';
+					$this->_finalbody .= '--'.$boundary.'--';
 				}
 
 				return;
 
-			case 'plain-attach' :
+			case 'plain-attach':
 
-				$hdr .= 'Content-Type: multipart/'.$this->multipart.'; boundary="'.$this->_atc_boundary.'"';
+				$boundary = uniqid('B_ATC_');
+				$hdr .= 'Content-Type: multipart/mixed; boundary="'.$boundary.'"';
 
 				if ($this->_get_protocol() === 'mail')
 				{
@@ -1377,59 +1342,83 @@
 
 				$body .= $this->_get_mime_message().$this->newline
 					.$this->newline
-					.'--'.$this->_atc_boundary.$this->newline
+					.'--'.$boundary.$this->newline
 					.'Content-Type: text/plain; charset='.$this->charset.$this->newline
 					.'Content-Transfer-Encoding: '.$this->_get_encoding().$this->newline
 					.$this->newline
 					.$this->_body.$this->newline.$this->newline;
 
-			break;
-			case 'html-attach' :
+				$this->_append_attachments($body, $boundary);
 
-				$hdr .= 'Content-Type: multipart/'.$this->multipart.'; boundary="'.$this->_atc_boundary.'"';
+				break;
+			case 'html-attach':
+
+				$alt_boundary = uniqid('B_ALT_');
+				$last_boundary = NULL;
+
+				if ($this->_attachments_have_multipart('mixed'))
+				{
+					$atc_boundary = uniqid('B_ATC_');
+					$hdr .= 'Content-Type: multipart/mixed; boundary="'.$atc_boundary.'"';
+					$last_boundary = $atc_boundary;
+				}
+
+				if ($this->_attachments_have_multipart('related'))
+				{
+					$rel_boundary = uniqid('B_REL_');
+					$rel_boundary_header = 'Content-Type: multipart/related; boundary="'.$rel_boundary.'"';
+
+					if (isset($last_boundary))
+					{
+						$body .= '--'.$last_boundary.$this->newline.$rel_boundary_header;
+					}
+					else
+					{
+						$hdr .= $rel_boundary_header;
+					}
+
+					$last_boundary = $rel_boundary;
+				}
 
 				if ($this->_get_protocol() === 'mail')
 				{
 					$this->_header_str .= $hdr;
 				}
 
+				strlen($body) && $body .= $this->newline.$this->newline;
 				$body .= $this->_get_mime_message().$this->newline.$this->newline
-					.'--'.$this->_atc_boundary.$this->newline
+					.'--'.$last_boundary.$this->newline
 
-					.'Content-Type: multipart/alternative; boundary="'.$this->_alt_boundary.'"'.$this->newline.$this->newline
-					.'--'.$this->_alt_boundary.$this->newline
+					.'Content-Type: multipart/alternative; boundary="'.$alt_boundary.'"'.$this->newline.$this->newline
+					.'--'.$alt_boundary.$this->newline
 
 					.'Content-Type: text/plain; charset='.$this->charset.$this->newline
 					.'Content-Transfer-Encoding: '.$this->_get_encoding().$this->newline.$this->newline
-					.$this->_get_alt_message().$this->newline.$this->newline.'--'.$this->_alt_boundary.$this->newline
+					.$this->_get_alt_message().$this->newline.$this->newline
+					.'--'.$alt_boundary.$this->newline
 
 					.'Content-Type: text/html; charset='.$this->charset.$this->newline
 					.'Content-Transfer-Encoding: quoted-printable'.$this->newline.$this->newline
 
 					.$this->_prep_quoted_printable($this->_body).$this->newline.$this->newline
-					.'--'.$this->_alt_boundary.'--'.$this->newline.$this->newline;
+					.'--'.$alt_boundary.'--'.$this->newline.$this->newline;
 
-			break;
+				if ( ! empty($rel_boundary))
+				{
+					$body .= $this->newline.$this->newline;
+					$this->_append_attachments($body, $rel_boundary, 'related');
+				}
+
+				// multipart/mixed attachments
+				if ( ! empty($atc_boundary))
+				{
+					$body .= $this->newline.$this->newline;
+					$this->_append_attachments($body, $atc_boundary, 'mixed');
+				}
+
+				break;
 		}
 
-		$attachment = array();
-		for ($i = 0, $c = count($this->_attachments), $z = 0; $i < $c; $i++)
-		{
-			$filename = $this->_attachments[$i]['name'][0];
-			$basename = ($this->_attachments[$i]['name'][1] === NULL)
-				? basename($filename) : $this->_attachments[$i]['name'][1];
-
-			$attachment[$z++] = '--'.$this->_atc_boundary.$this->newline
-				.'Content-type: '.$this->_attachments[$i]['type'].'; '
-				.'name="'.$basename.'"'.$this->newline
-				.'Content-Disposition: '.$this->_attachments[$i]['disposition'].';'.$this->newline
-				.'Content-Transfer-Encoding: base64'.$this->newline
-				.(empty($this->_attachments[$i]['cid']) ? '' : 'Content-ID: <'.$this->_attachments[$i]['cid'].'>'.$this->newline);
-
-			$attachment[$z++] = $this->_attachments[$i]['content'];
-		}
-
-		$body .= implode($this->newline, $attachment).$this->newline.'--'.$this->_atc_boundary.'--';
 		$this->_finalbody = ($this->_get_protocol() === 'mail')
 			? $body
 			: $hdr.$this->newline.$this->newline.$body;
@@ -1439,6 +1428,57 @@
 
 	// --------------------------------------------------------------------
 
+	protected function _attachments_have_multipart($type)
+	{
+		foreach ($this->_attachments as &$attachment)
+		{
+			if ($attachment['multipart'] === $type)
+			{
+				return TRUE;
+			}
+		}
+
+		return FALSE;
+	}
+
+	// --------------------------------------------------------------------
+
+	/**
+	 * Prepares attachment string
+	 *
+	 * @param	string	$body		Message body to append to
+	 * @param	string	$boundary	Multipart boundary
+	 * @param	string	$multipart	When provided, only attachments of this type will be processed
+	 * @return	string
+	 */
+	protected function _append_attachments(&$body, $boundary, $multipart = null)
+	{
+		for ($i = 0, $c = count($this->_attachments); $i < $c; $i++)
+		{
+			if (isset($multipart) && $this->_attachments[$i]['multipart'] !== $multipart)
+			{
+				continue;
+			}
+
+			$name = isset($this->_attachments[$i]['name'][1])
+				? $this->_attachments[$i]['name'][1]
+				: basename($this->_attachments[$i]['name'][0]);
+
+			$body .= '--'.$boundary.$this->newline
+				.'Content-Type: '.$this->_attachments[$i]['type'].'; name="'.$name.'"'.$this->newline
+				.'Content-Disposition: '.$this->_attachments[$i]['disposition'].';'.$this->newline
+				.'Content-Transfer-Encoding: base64'.$this->newline
+				.(empty($this->_attachments[$i]['cid']) ? '' : 'Content-ID: <'.$this->_attachments[$i]['cid'].'>'.$this->newline.$this->newline)
+				.$this->_attachments[$i]['content'].$this->newline;
+		}
+
+		// $name won't be set if no attachments were appended,
+		// and therefore a boundary wouldn't be necessary
+		empty($name) OR $body .= '--'.$boundary.'--';
+	}
+
+	// --------------------------------------------------------------------
+
 	/**
 	 * Prep Quoted Printable
 	 *