This protocol extends message-id that is defined in [RFC2822]. In this protocol, the Message-ID header indicates that the Internet message is an alert (1) by beginning with a left angle bracket (<) and the alert GUID. The alert GUID is fixed for all alerts (1) and has the value "3BD50098E401463AA228377848493927".
alert-message-id = "Message-ID:" alert-msg-id CRLF alert-msg-id = [CFWS] "<" alert-guid "-" id-left "@" id-right ">" [CFWS] alert-guid = "3BD50098E401463AA228377848493927" id-left = dot-atom-text / no-fold-quote / obs-id-left id-right = dot-atom-text / no-fold-literal / obs-id-right
To show that the Message-ID header in this protocol is an extension of Message-ID in [RFC2822], [RFC2822] section 3.6.4 defines a message-id as follows:
message-id = "Message-ID:" msg-id CRLF msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS] id-left = dot-atom-text / no-fold-quote / obs-id-left id-right = dot-atom-text / no-fold-literal / obs-id-right
Based on the preceding definitions of alert-message-id and message-id, if alert-guid is considered as a portion of id-left, an alert (1), represented by alert-message-id, conforms to the definition of message-id.
The Message-ID header MUST be present. If alert-message-id as defined earlier is present in Message-ID, the protocol client considers the Internet message as an ALERT and processes the additional alert metadata in the headers as defined in X-AlertId (section 2.2.2) through X-Sharing-Title (section 2.2.11).