I wouldn't personally recommend auto correcting the email address' domain name, but you could check it against the "VALID" domain name extension, and for that you need to check it against list of valid domain name extensions which would be an absolute pain, specially nowadays that we have new and totally weird domain name extensions, here is a link to all of them; http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains
However personally I wouldn't recommend neither of the domain and its extension as it could be a pain, also you'll be confusing the user... and if something isn't working properly as it should then you'll lose your new user and they'll never ever come back again... trust me!
As so many people suggested, I would highly recommend agree with the "Did you mean .com?" as 1) you're constantly giving feedback, 2) they can still change it if it isn't correct, and 3) you're not over complicating things for both your app/website or whatever is and the user, 4) less http requests, less page loads by ajax or whatever that u be using to check in the background, 5) most importantly less work/code...
I hope it helps :)