I am looking for a way to validate the DKIM signature of the incoming email.
I know how to do it in Java SE but it will use classes like javax.naming.directory.DirContext to get data from DNS server and this class is not white listed in App Engine.
Any idea how to communicate with DNS form Google App engine?
There is a blog post that says:
Once you've configured DKIM, just send an email from your Google Apps account to:
dkim@dkim-test.appspotmail.com
within minutes, you should get back an email that says "PASS" or "FAIL". If your test passed, you're all set!
I tried it and it works! It seems like a Google App Engine Application. How is it done?!
I'm the author of the dkim-test app. Unfortunately I did not actually find a native way to do DNS queries in AppEngine. There's a feature request in the AppEngine issues tracker here:
http://code.google.com/p/googleappengine/issues/detail?id=354
The way I got around this for dkim-test was to do a HTTP GET request to http://whatsmyip.us/dns_txt.php?host=google.com (where google.com is the host I want to retrieve TXT records for).
Obviously there are some down sides here. dkim-test is entirely dependent on whatsmyip.us to work, should that service go down or they decide to block dkim-test, then it would break. Things would also break if they changed the format of the response.