I'd like to have emails to a given domain, say http://mydomain.com/, processed by an AppEngine app, let's call it http://emailprocessor.appspot.com/ .
That is, an email to "hello@mydomain.com" should be received and processed by emailprocessor.appspot.com as if it was an email to "hello@emailprocessor.appspot.com" .
I imagine I could do this via MX records for my mydomain.com domain, but I can't find instructions anywhere.
Is this possible, and if so does one set it up?
Also there is no direct support for this according to documentation
BUT
if your http://mydomain.com/ hosted on google apps and you create user hello@mydomain.com as gmail account and in it configure email forwarding rule to the "hello@emailprocessor.appspotmail.com" it should work as it works for any general gmail account email forwarding. It preserves original headers like sender etc.
I almost sure that most of other mail services or servers can support this feature. check documentation of your mail service.
PAY ATTENTION! it must be emailprocessor.appspotmail.com note the appspotmail.com not appspot.com
I did not try it myself yet so I will be happy if you confirm that this works. Again it should.
What I have done is to point the MX record to a server that allows you to do email domain forwarding. Then you can forward all emails to emailprocessor.appspotmail.com.
The advantage of this is that you catch all usernames: hello@mydomain.com, goodbye@mydomain.com, etc...
If your host has cPanel see this: http://www.siteground.com/tutorials/email/email_domain_forwarding.htm
No, there's no documented support for receiving mail on a custom domain.
You would need to host mail elsewhere and configure a forwarder to emailprocessor.appspotmail.com.