Mullion Privacy Policy

Effective date: 1 October 2026

Who is responsible

Mullion is made by i4x Studio, a business registered in Poland (CEIDG), NIP 1182004411. Contact: support@i4xstudio.com.

Summary

Mullion turns a 5K iMac into a second display for another Mac. It has two apps: Mullion Display on the Mac you work on, and Mullion Receiver on the iMac. They talk only to each other over your local network, through an encrypted connection, except for the license checks described below. i4x Studio receives none of your screen content or input.

What the apps access

• Your screen, on the sending Mac. Mullion Display captures what is shown on the display it streams, using macOS screen capture, which requires your permission. Captured video goes only to the paired iMac and is not recorded or stored.
• Keyboard and mouse, both ways. So that the iMac's keyboard and mouse can control the other Mac, Mullion Receiver needs Accessibility and Post Events on the iMac, and Mullion Display needs Accessibility on the sending Mac. These permissions let the apps read and send key presses and clicks; the apps use them only to pass input between the two paired Macs. Screen Recording is required separately, for the screen capture described above. You can withdraw each permission in System Settings › Privacy & Security, or on macOS 12 in System Preferences › Security & Privacy › Privacy.
• Local network. Mullion Receiver announces itself on your local network so Mullion Display can find it. The two Macs pair once with a six-digit code shown on the iMac, valid for five minutes, and from then on connect over TLS encryption keyed by that pairing. They stream over Ethernet when connected, otherwise over Wi-Fi. You can make the iMac forget a paired Mac at any time; it must then pair again.

Pair when you trust the network you are on: someone recording your local network traffic at the moment of pairing could work out the code.

License checks

When you enter a license key, Mullion Display contacts Polar (polar.sh), our payment and licensing provider, to activate it. It sends the license key and your Mac's Computer Name, so you can recognise the Mac in Polar's customer portal. It then checks the license with Polar when it starts and once a week, sending the key and an activation ID, and contacts Polar again if you deactivate the license on this Mac. Nothing else is sent: no hardware identifiers and no usage data. The key, the activation ID, the email address on your purchase, and the time of the last check are stored in your Mac's Keychain. Purchases are handled by Polar under its own terms and privacy policy. Mullion Receiver makes no license checks.

What stays on your Macs

Settings are stored in each Mac's user preferences. Each app keeps a log and connection statistics in ~/Library/Logs on its own Mac; the logs show only a masked form of your license key.

Deleting your data

Delete both apps, their preference files in ~/Library/Preferences on each Mac, and their log files in ~/Library/Logs to remove all settings, the pairing, and the logs. To remove the license from this Mac and from Polar's list of activated Macs, deactivate it in Mullion Display before deleting the app. Remove the permissions in System Settings › Privacy & Security, or on macOS 12 in System Preferences › Security & Privacy › Privacy.

Your rights

Your screen content, input, and network traffic never reach i4x Studio. If you buy a license, Polar processes the purchase under its own terms and privacy policy and shares with i4x Studio the order and license details needed to support you, such as your email address, which we use only for that. Your rights over this data, and how to complain to the supervisory authority, are described in the website privacy policy at https://i4xstudio.com/privacy/, which also covers any email you send us.

Changes

We will post any change to this policy on this page and update the effective date.