How to limit GAE Emails to stay under email quotas

Question

I'm working on an GAEJ application which will email out on both an event basis and on a regular basis.
My current problem is that I'm having difficulty thinking of the best way to keep a track of where I am with each quota. I had hoped to try and access appstats in my code to check the total number of mail.send calls in the last minute & that day but the documentation of that code is rather lacking.

Any advice would be appreciate, cheers.

Answer 1

One way could be to keep a count in the memory cache for each quota day. Each of these counts would need to be backed by a datastore sharded counter for when/if the memory cache counts are evicted.

Answer 2

As Ian suggests, you could keep track of the number of mails sent through a counter. If there are numerous mails, consider using sharded counters.

Another option is to put the messages in a task queue, and to limit the output of the task queue to 100 messages per day (if you want to stay under the free quota). That way if a message cannot be sent today, it will be sent tomorrow.

To enforce another quota such as the 8 messages/minutes or the 8 attachements/minute, you can simply chain the task queues : a first one with a rate of 100/day, then another one with a rate of 32/min. That way you're in complete control of you quotas.

Caveats :

• To match the way Google computes the quotas, you must create one task per recipient, so for one mail sent to 4 recipients, you will create 4 tasks
• If you send too many mails, the task queues can become clogged (they empty more slowly than they are filled). So you have to watch the numbers of tasks.