iOS 11 adds a new SMS filtering feature that allows you to automatically filter spam text messages in the Messages app. It works similarly to the call-blocking feature added in iOS 10. Once activated, you'll have two tabs in your Messages app—one for real messages and one for "SMS Junk".

How It Works (and What You Need to Know About Privacy)

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Like call blocking, this feature requires you install a third-party app to do the filtering for you. When you install an app and give it permission to filter your text messages, your iPhone will send some text messages to the app for filtering. Specifically, when you receive an SMS message, your iPhone will send the sender's phone number or email address and the contents of that SMS message to the service. However, your iPhone will not send your own phone number or email address along with it.

If you receive an SMS message from a person in your contacts or from a number you've replied to at least three times, it won't be sent to the filtering service and will be automatically trusted. So the service won't see all the messages you receive.

The app can choose to process SMS messages entirely on your iPhone, but it can also pass them to an online service for scanning. This will allow apps to analyze the contents of text messages and proactively block new spammers based on message content rather than simply blocking messages from a list of phone numbers.

The developers of Hiya, our recommended app, say that any SMS messages sent to Hiya for filtering are sent anonymously to Hiya's servers where they're marked as good or junk. Hiya says it does not store the contents of the messages it receives. However, if the fact that some of your text messages may be sent to an online service for filtering bothers you, you shouldn't enable this feature.

How to Enable SMS Filtering

RELATED: How to Automatically Block Spam Calls on an iPhone

There are a number of third-party apps that can perform the SMS filtering, but we like Hiya. Hiya was already our favorite for call-blocking on an iPhone, and now Hiya 4.0 can also filter SMS messages.

To enable this feature, install Hiya, then navigate to Settings > Messages > Unknown & Spam and enable the "Hiya" option under SMS Filtering. You will see a warning about the privacy issues involved in enabling this feature, which we explained above.

If you choose to install another SMS filtering app, you'll see it as an option on this screen instead.

You're now done. When you open the Messages app once again, you'll see your messages are filtered into two tabs: one for "iMessage & SMS", and one for "SMS Junk". You won't receive notifications when messages arrive and are put into the "SMS Junk" tab, although you can still go tap the tab and look through the messages to confirm no real messages were marked as junk, if you like.

How to Filter Unknown iMessage Senders

You can also choose to filter out messages from unknown senders in iMessage. On the Settings > Messages > Unknown & Spam screen, enable the "Filter Unknown Senders" option. Once you do, you'll have two tabs in Messages: One for "Contacts & SMS" and one for "Unknown & Junk".

This particular option will only filter out messages from unknown senders if they were sent via Apple's iMessage. SMS messages from phone numbers you've never contacted before will still be placed in the main tab.

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