drupal_html_to_text() can only run once

If D6 can't send more than HTML mail per page that's imo a critical problem

Why not add a $reset parameter? It would be much cleaner, and compared to that it is a minor API modification to solve a critical omission. (I would not expand logic to collect the fold the same URL, so let's keep focusing on adding a clean reset option).

In fact, it looks like _drupal_html_to_mail_urls() needs a $reset parameter and it needs to be reset before the call to preg_replace_callback($pattern, '_drupal_html_to_mail_urls', $string);

Quick note: The diff "-p" option (as far as I know) adds the relevant function name to each chunk. That makes it a lot easier to see what function is being changed and what their parameters are; I can only guess that the first one is html_to_text and the second one is the urls function.

Here is the approach I suggested, please review/test.

A simple script to test before and after the patch:

require_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

$text = '<a href="http://drupal.org">Drupal</a> test <a href="http://example.com">Example</a>';
echo drupal_html_to_text($text);
echo drupal_html_to_text($text);

Ok, confirmed the problem without the patch, applied the patch and did a few variation of the script. Things worked. :) RTBC.

Thanks, committed.