My apologies, I don't know if this is appropriate or not. I read vix.com/spam, and didn't see how to report rogue sites.
For now you just mail to scott@zorch.sf-bay.org. I'll recommend to him that he set up a more permanent reporting address -- we registered the abuse.net domain just for this kind of thing, but it's not being used much yet.
I've gotten spam from worldnet.att.com four times in the last four days.
Worldnet doesn't run Sendmail, which makes it harder for them to just upgrade to 8.8.5 (or even 8.8.4) and then to implement the recommendations in http://www.sendmail.org/antispam.html. However, they are working hard on turning off outside-to-outside relay support, which unfortunately happens to be an automated feature of most SMTP server software. Unofficial reports suggest that some time in mid-March they will be out of the spam relay biz. Note that in spite of this, I have blackholed their main mail server. I was getting 10 spams a day through them at one point. I guess the spammers figured that Worldnet was to big to block. (I guess they were wrong.)
I've received no response from postmaster, and any mail I send back to the site says that the mailbox is full, so the message won't be delivered.
Indeed. They're aware of the problem, their mailbox is full of other complaints.
So, in future, how do I report a rogue site? Should I simply mail scott mueller?
For now, yes. It'll probably show up as report@abuse.net soon, though. NANOG is not the right place to discuss this. See the usenet newsgroups related to network abuse.