Understanding the Unknown Senders inbox on iOS and how it affects RCS

RCS messages are sent from a separate Sender ID (RCS agent) rather than the phone number or short code used for SMS. Because of this, messages are treated as coming from a new sender in the recipient’s messaging app, which will affect where they appear on iOS devices with the Unknown Senders filter enabled.

How the Unknown Senders inbox works

On iOS, users can enable a setting called Filter Unknown Senders, which separates messages from numbers or senders not saved in their contacts and with whom they have not previously engaged.

• This setting is off by default, meaning most users will receive all messages in their primary inbox.
• When on, the first message from a new Sender ID (e.g. RCS agent) appears in both the primary and unknown senders inboxes, allowing the recipient to review it and mark the sender as known.
• If the recipient marks the sender as known, all future messages from the SID (e.g. RCS agent) will appear in the primary inbox.
• If they do not, any future messages from that Sender ID (e.g. RCS agent) will appear only in the unknown senders inbox.
• Any response to a message will move the thread to the primary inbox.

Note. Apple has not publicly confirmed how older threads are handled. However, based on our testing, threads with user responses appear in the primary inbox, while those without responses appear in the unknown senders inbox.

Contact Cards

Unlike SMS senders, RCS agents cannot be saved as contacts on a user’s device. As a result, contact cards are not supported on RCS.

If any of your existing flows include contact cards, they will be automatically removed from the RCS version of the message to avoid delivery issues.

You should update these flows by either:

• Editing the RCS version of the message to remove references to saving the sender as a contact and instead ask users to mark the sender as known, or
• Using a conditional split to prevent the message from sending to RCS recipients altogether.

Recommended best practices

To maximise visibility and keep your RCS messages in the primary inbox, send an interactive first message such as a welcome message with Quick Replies. When a recipient responds, the sender is automatically classified as known, ensuring future messages stay in their main inbox.

Summary

• RCS messages are sent from a new Sender ID (RCS agent).
• RCS agents cannot be saved as contacts, and contact cards are not supported.
• The Unknown Senders filter is off by default, but when enabled, it moves messages from unsaved contacts that a user has not engaged with into the Unknown Senders inbox.
• Encourage engagement using interactive messages to ensure future messages appear in the primary inbox.