Many users are complaining that mass email isn't working after upgrade to v3.0.4 and I think someone mentioned it didn't work after upgrading to v3.0.3. I had the same problem and the only solution I have found to fix the problem satisfactorily is by using third party SMPT.

Here is one of many links on the subject: http://www.phpbb.com/community/viewtopic.php?f=46&t=1356535

Are you aware of this and if so is it in the pipeline to be fixed?

Cheers, Mix