More efficient to store email addresses or query facebook for email when sending bulk emails

I have a facebook application which I communicate directly with users via email. Is it a better idea to store the user's email addresses when they authenticate the application and send an email to ever user in my database

or

should I just store the fbid and execute a query for each user at the time of sendi开发者_运维技巧ng the emails to get the latest possible email address from facebook? This could be much slower, especially if I'm sending out 10,000 emails, but it will give me the latest email addresses in the event a user has changed theirs.

Which one is best?

I would say it is best to store the users email address locally and then subscribe to Facebook real time updates for when the user updates their email address.

I will warn you that you run the risk of having your Facebook app removed due to spam if you are sending unsolicited non-opt-in marketing emails (spam) to users and the way Facebook will know is it too many people deactivate your application or report it as spam.

The issue with querying Facebook for users' email addresses is that the users need to give you permission, and that will stop users from granting your app permissions. In toehr words they will not use your app.

Zynga handles this by having a post-joining step where the user gives the app permission, possibly after playing for some time and building some trust. Then they just re-authenticate with the right permissions and they have access to the email address.

Apart from the the performance shouldn't be too much of an issue. You might update every email address weekly or daily. Probably better than as you need it.

The other option is to get users to endter their email addresses, which is the second option you mention. How this works will depend on your app and the users, since people may be reluctant to give you their email address. Some will and some won't.

My advice is, either way, don't make it mandatory. If your app needs the email address, redeign your app (if possible).