+1 on Nicola's answer. App Engine will make outgoing HTTP requests from a subset of the addresses returned by the TXT records. Note that these can change at any time, so you can't simply fetch the list as it stands now and assume that will continue to be the case.
IP-based authentication is a poor choice here, as you will open yourself up to access by any App Engine application. Instead, you should implement a proper authentication system and use that instead of relying on IP ranges for your security. See original post. <https://groups.google.com/forum/#!topic/google-appengine/-aOmrzxLPAM> -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/d1df6c55-c0b4-4578-b583-64acf5399122%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
