Index: mimemail.inc
===================================================================
RCS file: /cvs/drupal/contributions/modules/mimemail/mimemail.inc,v
retrieving revision 1.41
diff -u -r1.41 mimemail.inc
--- mimemail.inc	24 Mar 2010 21:36:41 -0000	1.41
+++ mimemail.inc	8 Apr 2010 18:46:47 -0000
@@ -87,11 +87,22 @@
   $pattern = '/(<link[^>]+href=[\'"]?|<object[^>]+codebase=[\'"]?|@import |src=[\'"]?)([^\'>"]+)([\'"]?)/mis';
   $html = preg_replace_callback($pattern, '_mimemail_replace_files', $html);
 
-  $document = array(array(
-    'Content-Type' => "text/html; charset=utf-8",
-    'Content-Transfer-Encoding' => '8bit',
-    'content' => $html,
-  ));
+  $chopped_html = chunk_split_for_8bit_encoding_xfer($html);
+  if ($chopped_html == FALSE) {
+  // 8bit encoded trasnsfer may not be safe (CR/LFs could be inserted where not desired)
+    $document = array(array(
+      'Content-Type' => "text/html; charset=utf-8",
+      'Content-Transfer-Encoding' => 'base64',
+      'content' => chunk_split(base64_encode($html)),
+    ));
+  }
+  else {
+    $document = array(array(
+      'Content-Type' => "text/html; charset=utf-8",
+      'Content-Transfer-Encoding' => '8bit',
+      'content' => $chopped_html,
+    ));
+  }
 
   $files = _mimemail_file();
 
@@ -593,3 +604,60 @@
 
   return FALSE;
 }
+
+/**
+ * Here you can adjust the max. chunk length (in characters) and max. number of 
+ * chunks. Be aware that 1 character in UTF-8 encoding is 1 - 4 octets long, and
+ * SMTP transfer is limited to the maximal length of 998 octets within 1 chunk 
+ * (so if you are using only common characters (1 or 2 bytes long), you can try 
+ * to increase this limit to approx. 500, but be aware that you may get some 
+ * CR/LFs where not desired; with default value 248 you are on the absolutely 
+ * safe side (even if all characters are 4 Bytes long)
+ */
+function chunk_split_for_8bit_encoding_xfer($string) {
+  $char_limit = 248;
+  $loop_limit = 1000;
+
+  // Nothing to touch below this line...
+  $return_string = "";
+  $loop = 0;
+
+  while (strlen($string) > $char_limit && $loop < $loop_limit) {
+    $tmp = substr($string, 0, $char_limit);
+
+    if ($to = strrpos($tmp, "\r\n")) {
+      // If there are 1 or more CR/LFs, just continue at the last one...
+      $return_string .= substr($string, 0, $to + 2);
+      $string = substr($string, $to + 2);
+      $loop++;
+    }
+    elseif ($to = strrpos($tmp, "\n")) {
+      // We try Unix line breaking (LF only) first; if found, replace the last
+      // LF (within the max. chunk length) with CR/LF (or, should we append it?!)
+      $return_string .= substr($string, 0, $to) . "\r\n";
+      $string = substr($string, $to + 1);
+      $loop++;
+    }
+    elseif ($to = strrpos($tmp, " ")) {
+      // We try a space at the end; here, we append CR/LF as they should both be
+      // displayed as a single space (or, do we have to replace it?!)
+      $return_string .= substr($string, 0, $to + 1) . "\r\n";
+      $string = substr($string, $to + 1);
+      $loop++;
+    }
+    else {
+      // We can not safely chop HTML file, give up...
+      $loop = $loop_limit;
+    }
+  }
+
+  if ((strlen($string) < $char_limit + 1) && $loop < $loop_limit) {
+    // Append the residual chunk and return chopped HTML file...
+    $return_string .= $string;
+    return $return_string;
+  }
+  else {
+    // We can not safely chop HTML file; return error...
+    return  FALSE;
+  }
+}