Messages sent to the business are encrypted between the user’s device and Apple’s messaging servers, using the same security and Apple messaging servers as iMessages. Apple messaging servers decrypt these messages in RAM, and relay them to the business over an encrypted link using TLS 1.2. Messages are never stored in unencrypted form while transiting through the Apple Messages for Business service. Businesses’ replies are also sent using TLS 1.2 to the Apple messaging servers, where they are encrypted using the unique public keys of each recipient device.
If user devices are online, the message is delivered immediately and isn’t cached on the Apple messaging servers. If a user’s device isn’t online, the encrypted message is cached for up to 30 days to enable the user to receive it when the device is back online. As soon as the device is back online, the message is delivered and deleted from cache. After 30 days, an undelivered cached message expires and is permanently deleted.