LLM and Google are suggesting it might be this https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxmsg/b046868c-9fbf-41ae-9ffb-8de2bd4eec

LLM and Google are suggesting it might be this https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxmsg/b046868c-9fbf-41ae-9ffb-8de2bd4eec82 https://learn.microsoft.com/en-us/openspecs/exchange_server_... A lot of Microsoft formats are open standards... Created by and only used by Microsoft...