X-apple-i-md-m ^hot^ <Reliable>

The data usually consists of:

x-apple-i-md-m wasn't a pulse. It was a footnote in a million-line server log from a defunct Apple relay station in Novosibirsk. The ‘i’ likely stood for ‘iPhone’ or ‘iMessage’. ‘MD’ could be ‘Mobile Device’ or ‘Medical Data’. ‘M’ might be ‘Metadata’. It was garbage.

In technical terms, it is a piece of "anisette data" that provides to Apple’s servers during the login process. It works alongside other headers to verify the device's identity:

Ensures the request originates from a trusted Apple device or a provisioned Windows PC.