Receive Email address count limit in app engine

My mail is regarding the option for receiving email to any address which looks like - xxx@appid.appspotmail.com documented here: http://code.google.com/appengine/docs/python/mail/receivingmail.html

My questions are:

1. Is there any restriction on the number of email addresses which can be created using the above format and used inside the application? As an example I may have a million users and could have some sort of a "in-mail" facility where each user is assigned a unique "xxx" id.

2. Is there any limit on the number of emails which can be received by an address of the above format? I don't see any quota restrictions speci开发者_运维知识库fied anywhere?

There's no limit to the number of email addresses you can send or receive email on. Incoming email is simply sent to your handler with the address preserved; no accounts get created, so there's no reason to limit the number of unique addresses. The system-wide quota limits on incoming mail, total requests, and calls to the mail API are the only ones that apply here.

There is no limit on the number of addresses where your app can receive mail, or the number of emails it can receive.

App Engine does not persist the addresses you've used to receive mail; each inbound message is handled like an HTTP POST and then discarded. Sending a million emails to one address or a to million addresses will use the same resources.

The mail-related quotas apply to sent mail only. For CPU, bandwidth, etc., inbound mail draws from the same resource pool as your HTTP requests. There's no indication in the docs of any quota specific to inbound mail.

I can't see any mention of a maximum of email addresses you can have in the format string@ appid.appspotmail.com. But surely there must be some internal limit specified. I guess the appspotmail option is not meant to be used to create unique emails for each of your app's users (especially if you have a large number of users).

There are limits specified in the quotas, for example you can send mails to a maximum of 7,400,000 recipients a day, and you can make a maximum of 1,700,000 calls a day to the GAE Mail API (both limits apply only when billing is enabled). So if you had a million users, you probably would reach the API limit pretty soon when most of them would receive one or multiple emails.