How to send mail to all users in an app engine application - google-app-engine

Question

I work on a google app engine application which currently has about 4000 users and I want to write a handler to send email to all users.
The problem is that app engine has limitations on getting entities from datastore. For example, the max number of rows which can be returned from datastore is 1000.
I can get all users incrementally by using a loop and limit, offset parameters of gql. But this time the max lifetime of a handler which is 30 seconds limits me.
I made some research to overcome this problem and I have ended up with backends. But it seems to me backends usage is different I mean it is not appropriate for this operation.
How can I achieve this task?
Thanks in advance..

Answer 1

from google.appengine.api import mail
mail.send_mail(sender="Example.com Support <support#example.com>",
to="Albert Johnson <Albert.Johnson#example.com>",
subject="Your account has been approved",
body="""
Dear Albert:
Your example.com account has been approved. You can now visit
http://www.example.com/ and sign in using your Google Account to
access new features.
Please let us know if you have any questions.
The example.com Team
""")

Answer 2

Task Queues give you a 10-minute deadline. See the documentation

Answer 3

You can get more than 1000 items in one request. Just avoid using fetch and try this:
entities = Entity.all() # <-- no fetch
for e in entities:
mail.send_mail()
This will keep on getting users until the 10 minute limit run out: a lot of entities and more than enough for 4000 users.