Advice for APNS push server for new email notifications

How would you implement an APNS server that checks for new email and sends a push notification to an iPhone when one is detected? I am wondering more at an architectural level. For the sake of simplicity, let's say we're building a push server for gmail. The challenges that I can see are:

• How do you continuously poll Gmail for potentially tens of thousands of unique email accounts for new mail? Would gmail even allow this from a single set of IPs?

• Gmail has an IMAP and Inbox feed. In order to detect if a new piece of mail has arrived, would you need to remember the last email that was received (or pushed) for each account?

• Would the CPU cycles and bandwidth required for this continuous polling make a cloud solution such as EC2 or RackSpace affordable?

• How do you handle authentication and authorization in a secure fashion? For example, I once used a gTalk client on my iPhone which had push notifications and Gmail warned me the next time that I logged in from the web interface that my account was accessed from an unusual IP. Is there a way to avoid this? Would you store the user's credentials on the server? An OAuth token?

I should mention that this is to please my personal curiosity but it might als开发者_开发技巧o be an interesting project for learning to program in Erlang.

Any insight on this would be greatly appreciated.

You might want to check this:

http://code.google.com/apis/gmail/