Notification Settings — Limit Push Folders #11684

Users can currently turn on push notifications on too many folders. While these settings are buried, making them more difficult to mess up, a user could end up turning on push on too many folders, which can cause email delivery issues.

This is because our "Push" notifications aren't traditional "push" notifications. Push goes through Apple or Google servers to display. We don't do that because we care about privacy. Instead, we directly contact the email hosting service and, if a new change is found, we notify the user with a local notification.

When fetching, this is fine. We can fetch as many folders and from as many accounts as we want. However, for push, we're using IMAP IDLE. IMAP IDLE works by keeping a port open to observe changes on the server. This includes new emails coming in. However, services limit the number of IMAP IDLE connections we can maintain. It's different for each service, and we cannot query this limit.

Some services allow only 2 open connections. Others up to an outstanding 15. Most commonly, email services allow 2-3, with this including Gmail at 3. Outlook seems to be around 8, and Apple's iCloud mail could be as high as 15, though reports are mixed. This may also be different if the user uses email masks, has multiple sub accounts, has a business account, or has certain settings enabled. As such, we can never predict how many folders are allowed to be open to IMAP IDLE syncing.

Failure states for selecting too many folders are not good. We don't get a detailed error from the server as to why we can't sync. To the user, it's just a server authentication error. This is sub-optimal.

Instead, we'll set a limit on the number of folders they can enable. We suspect fewer users will access these features anyway, as we're adding the global sync switch in Notifications & Sync settings.

We will need to decide if this should be a soft or hard limit:

• Option 1: hard limit of 2 folders per account
• • Users who know their account can support more will be frustrated if they do a lot of server-side sorting and want all of their emails to sync
• • • We could trigger a fetch on any sync change, but this would impact battery life
• • Users would never get an inexplicable failure related to the account not being able to sync.
• Option 2: Soft Limit of 2 folders per account
• • This is likely the better option. After a user has already selected 2 folders for push syncing, we display a warning in the folder settings for notification and syncing to let users know that selecting more than 2 folders could create a failure, and they may have to clear these out if syncing fails.

I believe we're more aligned with the second option. This would be done with a subtitle under the push switch in the more specific per-folder settings.