That didn't work either, but I think I might know what the problem is: I installed the forum on a subdomain 'hybrids.mackrockets.com' from cPanel by telling it to use '../hybrids/forum/' for the path.
Looks like some of the phpbb functions work fine for
http://hybrids.macrockets.com/forum, but some are trying to access
http://macrockets.com/forum/
Did I foobar the install by putting it into a subdomain? If so, I think I can probably either find all the bad paths & correct them for the subdomain, or I could possibly live with the forum in the main path.
Not sure why this would affect the mailer tho... I still need to learn my way around, maybe check error logs?
TIA,