Mark,
I have been using phpBB for over two years at
http://www.bambooweb.info/bb/index.php
Are the emails being blocked by SPAMCOP? In my case I was bouncing emails that were to nonexistent addresses at my domain. I found out from the SpamCop website that the spammers forge the return addresses so when the email is bounced the person that received the bounced spam will report your domain.
If the emails that are being blocked are AOL addresses the only things we can do is to contact the web host when it happens and let them deal with AOL, Pay the "extortion" money to AOL to guarantee that the emails will go thru or ask the users to switch to a different email provider. About every two months AOL blocks my emails and I report it to my web host then it takes about a day before the emails start working to AOL addresses
One vital thing that I had to change in phpBB was how the database user is set up. My web host has a restriction on the 'max_questions' database parameter. This caused my forum to shut down under heavy use. (While I was on vacation
![Mad :x](./images/smilies/icon_mad.gif)
)If your web host does not limit this great but if they do you need to set up multiple users to spread out the load. I can send you an example of the code change to add users.
Another mod that I have done to my board is to automatically fill in the Subject line on replies which makes it easier to follow threads.
Bill