Thus spake "Edward B. DREGER" <eddy+public+spam@noc.everquick.net>
(Note that I've not examined OpenDNS's offering, so I'm _not_ pretending to comment on what they do.)
Let's quit looking at overly-simplistic correction mechanisms. Do spell checkers force autocorrection with only a single choice per misspelled word?
Ever used Word or Outlook? They annoyingly "fix" words as you type without offering multiple choices or even alerting the user that they're doing it. I've learned to re-read what I write several times now because I've been burned too many times by jargon being "corrected" to unrelated "real" words -- but I type "teh" and similar things often enough I can't afford to turn the feature off. (And my employer requires me to use those apps, so all you anti-MS folks please sit back down) OpenDNS's typo-fixing service can supposedly be turned off, but I don't see how that would work when you have multiple users behind a NAT or a recursive server. There also may be hidden problems if an ISP pushes all of their users onto this service and the users have no clue they've been "opted in" or how to opt back out (and we all know how well "opt out" systems work for email in general).
Return an A RR that points <correction service>-controlled system. Said system examines HTTP "Host" header, then returns a page listing multiple possibilities.
"The site you specified does not exist. Here is a list of sites that you may be trying to access: ..."
And that solves most of my objections, at least for HTTP. It still breaks a lot of other protocols.
I'm generally ignoring other protocols to limit the discussion scope. However, one can see how SMTP and FTP might be similarly handled. (IMHO not as good as a SRV-ish system that could return NXDOMAIN per service, but actually somewhat usable today.)
If web browsers consulted SRV records instead of blindly connecting to the A, that would appear to solve everything: NXDOMAIN for the A but the HTTP SRV could point to the typo-correction server. I'd not be inclined to argue with such a setup, but it requires a refresh of every browser out there, so it's not realistic. S Stephen Sprunk "Stupid people surround themselves with smart CCIE #3723 people. Smart people surround themselves with K5SSS smart people who disagree with them." --Aaron Sorkin