I was monitoring my email and RSS closely the night I sent the email. I had already written and proofread the real version, and written an email explaining I had discovered a mistake; so to change my site was just a matter of issuing a single revision-control command (darcs rollback) & re-syncing my site, and then sending the email. I don't think the bad version would have been up for more than 10 or 20 minutes past him posting or replying clearly that he would post it.