I posted this to the Joomla forum but so far no action on that post so I thought I'd try here.  I'm running the site on an LP shared hosting plan:

I'm pretty convinced there is a problem with the Mass Mail component.  I have joomla 1.0.11 running on a sub-domain to a main site that is also running Joomla but the main site install is 1.0.10.  Mass mail works fine on the main site but not on the sub-domain.  While it says that emails are sent no one is getting these.  However, email IS SENT when the Contact Form is submitted or a new users is registered.  I have tried all Mailer options.  The sendpath is set to the same as the main site (/usr/sbin/sendmail) so maybe that is a problem but since the other types of email are being sent this would appear not to be the problem.  I have not reset the Global setting (still ON) and RE_EMULATION is also not reset (still ON).   At this point I do not have a clue as to what is going on.

Hey Paul, maybe if you post some more details you will get somebody with some Joomla experience to help you out here.