autoresponders are likely to quote back (a) none of the received text, (b) all of the received text, or (c) a certain amount from the top of the received text. So if the applicant is sent two confirmation codes and in order to confirm has to return only the lower one without the upper one, a bot is likely to fail. Or if the confirmation code needs to be edited slightly -- say it is twelve characters long, and it has to be sent back with the first five characters moved to the end -- a bot is likely to fail.
With majordomo 1.x, replying to the confirmation message doesn't work. It usually puts ">" in front of the text to show it's quoted and that alone will cause majordomo to reject it (unknown command ">"). Also, the confirmation code is not the first line of the quoted text, which would also cause majordomo to reject it. There are plenty of humans who make this mistake.
...Bob
