I was under the understanding the issue you had was not being able to add enough forumids in the usergroup manager to the autosubscribe option.
Issues with the preg_match, things needing to be removed from the text of emails prior to posting or oddities in characters like %20 etc, will be resolved in the next version for 3.8 . I'll be going a new route of requiring the pear package for mimedecoding to be installed. I spent way too much time trying to work on the decoder. I'm going to focus on the integration for the next version. Please be patient on preg_match issues and worry not.. pear packages are extremely easy to install