Now I just have to delete the 2000 emails from WeBWorK I've received in the last week.
Bob
OK. Thanks to those who thought about this problem. It turned out to be a perl issue. When installing WeBWorK, our IT guy had to install the perl module Mail::Sender. Somehow in the process a file "Sender.config" got created in the perl library which contained defaults for both the bcc field and the reply-to field. These defaults were not being overridden by WeBWorK -- hence the strange behavior.