diff --git modules/mimemail_compress/mimemail_compress.inc modules/mimemail_compress/mimemail_compress.inc
old mode 100644
new mode 100755
index f0f91c7..0a04c92
--- modules/mimemail_compress/mimemail_compress.inc
+++ modules/mimemail_compress/mimemail_compress.inc
@@ -31,14 +31,22 @@ function mimemail_compress_clean_message($message) {
 class mimemail_compress {
   private $html = '';
   private $css  = '';
+  private $dom_class_available = FALSE;
 
   public function mimemail_compress($html = '', $css = '') {
     $this->html = $html;
     $this->css  = $css;
+    // check if DOM is available
+    $this->dom_class_available = class_exists('DOMDocument', FALSE);
   }
 
   public function compress() {
     error_reporting(0);
+    // if DOM is unavailable return the uncompressed html string
+    if(!$this->dom_class_available) {
+      return $this->html;
+    }
+
     $doc = new DOMDocument('1.0', 'utf8');
     $doc->strictErrorChecking = false;
     $doc->formatOutput = true;
diff --git modules/mimemail_compress/mimemail_compress.module modules/mimemail_compress/mimemail_compress.module
old mode 100644
new mode 100755
index 7065239..e4e2bc3
--- modules/mimemail_compress/mimemail_compress.module
+++ modules/mimemail_compress/mimemail_compress.module
@@ -17,3 +17,21 @@ function mimemail_compress_mail_post_process(&$message, $mailkey) {
   $output = $output->compress();
   $message = $output;
 }
+
+/**
+ * Implementation of hook_requirements().
+ */
+function mimemail_compress_requirements($phase) {
+  $requirements = array();
+  $t = get_t();
+  if ($phase == 'runtime') {
+    $dom_available = class_exists('DOMDocument', FALSE);
+
+    $requirements['mimemail_compress_DOMDocument_available'] = array(
+      'title' => $t('Mimemail Compress'),
+      'value' => $dom_available ? $t('DOMDocument class is available') : $t('Mimemail can\'t compress emails sent because you don\'t have XML-PHP library installed'),
+      'severity' => $dom_available ? REQUIREMENT_OK : REQUIREMENT_ERROR,
+    );
+  }
+  return $requirements;
+}