Mark just alerted me that he blocked an IP address because it was attempting to spam us. Or rather, it was attempting to spam all sorts of addresses to conman.org. Over 200 attempts in the past month.
I then started going through the mail logs, and I found all sorts of fun stuff. Mr. Spammer trying various userids. Then there was the spammer that attempted to mail the same invalid address nearly 300 times. I also noticed that spammers were queueing mail up at our backup MX servers, which not only loads our system up rejecting such mail, but loads our backup MX servers in accepting such mail to begin with.
Mark and I discussed the issue a bit and we came up with a few ideas of lessening the load. One idea was to add a module to Postfix (since not only do we use that, but both our backup MX servers use it as well) to monitor rejected addresses and if a single IP address attempts to deliver to too many bogus addresses, automatically block access from that address for a period of time (both the number of attempts, and the length of time of the block would be configurable).
The other problem is spam sent to bogus addresses at the backup MX servers; they have no idea which addresses are valid and which aren't, so all mail is accepted and queued up for final delivery. To get around that problem, another module could be added for the primary MX server to notify the backup MX servers of valid addresses; something similar to the way DNS updates changes from master to slave servers. Such a scheme certainly won't scale, but for the number of users we have (across our system, and our backup MX servers) it's servicable, and it would prevent the backup MX servers from queueing up mail for non-existent users.
In fact, now that I'm thinking about it, I wonder if this is how people selling lists of email addresses can “claim” that all the addresses are deliverable? Of course they're deliverable, if you send the email to a backup MX server, of course it's deliverable (for most—I'm sure there are a few exceptions).
But this is something I need to look into …
The Publix we shop at is at the corner of US-441 and 8th, pretty much west-south-west Boca Raton. I'm not familiar with what is west of US-441 since everyone I know who lives here in Boca lives east of us (with the exception of JeffK, who lives about a block west of the Facility in the Middle of Nowhere); there hasn't been much of a reason to go west.
But curiosity got the better of me.
I turned west onto 8th and followed it out.
It was an odd neighborhood. I'm used to seeing the occational mobile home park (this is, after all, Florida) but never one this size. The entire neighborhood, going back perhaps two, three miles, consisted of nothing but mobile homes. And they had definitely seen better days too.
The road finally ended about two, three miles past US-441 in what for South Florida passes for a rual area. I turned around, and took the first street going north. I was in an exploratory mood. Very quickly the scenery changed from run-down rual to upscale yuppidom. Taking the next left (west) at a large four lane road I've never heard of before, I saw well manicured lawns and stately Royal Palms lining the street, with the occasional shopping center. It must have turned north because I found myself crossing first Palmetto Park Rd (a major east-west road here in Boca Raton) and then ending at Glades Road (another major east-west road). I then figured I'd see just how far west I could go on Glades.
Not very far. About half a mile and it turned south. There was not much here yet, but there was heavy construction on the west side, what looked to be either a huge school, or maybe a mall (hard to tell). A street sign revealed that I was on University Drive (which is a major north-south road around Ft. Lauderdale) but that it ended at Palmetto. No choice but to head back east at this point.
It was strange, like finding another city when not expecting it.