The problem with the phpBB forum is that the notification emails, when you watch a forum, do not include the message. On Sourceforge you are also not able to install a digest modification, eg. http://phpbbservices.com/digests/
Therefore I thought it would be good to have an external script, that regularly checks for new posts and sends an email with the contents.
In the end, it was not too hard.
This only works for a public forum, where all posts are accessible by non-registered users.
There is the page search.php (eg.http://sourceforge.net/apps/phpbb/openpetraorg/search.php?&sr=topics&search_id=newposts) that shows all new posts.
I store each post that has been sent as an email with the post number in a text file.
Then the script fetches the page of the new posts, and checks each post if it has been sent already.
The script sends HTML emails, and even quoting blocks appear quite alright in my email client (google mail).
The script is also able to parse the posts of a thread that spreads across several pages.
You also might find the functions interesting to get the HTML code and to parse for code between the beginning and the end tag.
The script is available here: http://download.pokorra.de/coding/PHPBB_Digest_SF.php.txt
Feel free to use the script and to modify it.
