Nobody likes spam. So to avoid spam they either inflict pain on others, like with challenge/response systems that send endless challenges to me since “I” have sent them spam (From headers are so hard to fake? (I know this guy who automatically responds to all challenge/response systems (evil, but understandable))), or they use “greylisting”, which is harmless, supposedly.
It just means that mail takes a bit longer to deliver, right? The first time you try (on a unique from/to pair), your MTA gets told that it has to wait for a while.
So when I do a Gmane subscription handling session, I first fire off a bunch of subscription requests. Then, since so many list admins use greylisting now, I have to wait for fifteen minutes to complete the process. Meanwhile, I’ve gone on to do other things, or I’ve left for a holiday in a differerent country, so the process stops in the middle, and the person who requested the list gets all sad and stuff.
See what you’re doing, greylisters? You’re making Gmane users sad! For shame!