How to make friends a 'known' texter

Q: When my friend sends group texts, she is identified on my iPhone 6 as an "unknown sender," even though she's in my contacts list. This doesn't seem to happen when she sends an individual text to me. What's wrong?

Gini Dodds, St. Paul

A: The problem may be caused by different kinds of texts.

If the sender and all the recipients of a group text are using Apple devices, the text will be sent as a group iMessage. That travels through Apple's servers rather than a cellular service's. Apple says its system is faster and uses encryption to ensure privacy.

If the sender or anyone in the group is using a non-Apple device, the text is sent via conventional text messaging, which uses either the SMS (Short Message Service) or MMS (multimedia messaging service) formats that are used by nearly all cellphones. Both are transmitted through the servers of cellular providers and are not encrypted.

Your iPhone should be able to correctly receive texts in any of those formats, provided those features are turned on. To make sure, go to Settings, click Messages, then look at the "on-off switches" behind iMessage, SMS and MMS — all should display the color green.

So, why is your friend being identified as an "unknown sender"? Here are some possible reasons:

If so, you can try to fix it by turning off MMS and SMS messaging on your iPhone. Then turn off your phone, turn it back on and turn MMS and SMS messaging back on. (Leave the iMessage switch alone; there are too many repercussions if you turn it off.) Check the group text to see if the sender is identified.

• The sender's current phone number doesn't match the phone number in your contacts list (maybe she has a new number, or a glitch altered her old number.) Try creating a new contact for the "unknown sender," then give the new contact your friend's name. (Keep her existing contact, too. It doesn't matter if two contacts have the same name.) Check the group text again to see whether the sender is now correctly identified. If so, watch future group texts to make sure she continues to be identified.

• Your friend's cellular provider is the problem. Its servers are handling the SMS or MMS group text messages in a way that will always garble her phone number, meaning your iPhone can't recognize it. If that's the case, the cellular company will have to fix it.

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