Occasional email outages
Grumpy Monday-morning rant from Jed. Please disregard. Partly just the product of too little sleep.
There are at least two sites on the web (and I assume there are others as well) that maintain databases of sites believed to be spam generators.
For example, one such site (the ORDB) has a database of "open relays"—mail servers that will accept email from anyone and pass it along to anyone. Open relays are great for spammers; if you're a spammer, you can connect to an open relay and send all your spam, whereas a respectable ISP might prevent you from doing that.
So the open-relay database sites are doing a public service. They provide a list of open relays, and ISPs can use that list to bounce all mail that comes from an open relay. Presumably the owner of the open relay eventually figures out (via "my mail is bouncing" complaints from irate users) that there's a problem, and takes steps to stop the relay from being open.
There's one big problem with this: false positives. Three times now, Pair (my web host and email service provider) has been falsely listed on spammer databases because of Pair customers mistakenly believing Pair has a problem, which causes all mail originating from certain Pair machines to bounce when directed to ISPs that rely on the spammer databases to block spam. For example, yesterday Pair's relay got listed at the ORDB, which meant that a followup email I sent to an author bounced. I had absolutely no way to contact this author until the ORDB happened to get around to delisting Pair. (I could use papermail, but that would be a big pain.)
So why, you might ask, did the ORDB list Pair as an open relay in the first place? According to Pair, a Pair customer noticed that they could send mail through relay.pair.com, and reported it to the ORDB.
In case it's not clear, Pair customers are supposed to be able to send mail through relay.pair.com. That's exactly why relay.pair.com exists. People who aren't Pair customers can't send mail through it.
Fortunately, the listing has been removed, and all should be fine now. But it's yet another thing you should be aware of if you're expecting mail from me at any given time: I have no control over Pair customers reporting their own mail service provider as a spammer because they don't understand what's going on. (The previous two times, unrelated to open relays, a Pair customer whose mail is forwarded through Pair to another address thought that the spam that was being forwarded to them was originating at Pair, so they reported Pair to spamcop, a blacklist site. Grr.) So sometimes I'll be completely unable to send mail to certain places.
(This morning I came up with a couple of alternative approaches; for example, I could have asked Susan to send the mail, and I probably could've sent it in a way that didn't use relay.pair.com. But see above about big pains.)
This sort of thing is why I don't like systems that silently dispose of messages they consider spam. If there's no human oversight, chances are good that there will be false positives. (Even if there is a human involved, of course, there are bound to be false positives; but I'm a lot more comfortable relying on my own sense of what constitutes spam than letting a software filter decide for me. Or rather, the software filter makes a first-pass approximation, but then I look over the results to be sure it was right, rather than just throwing away anything the software considers spam.)