1. In a computer system that is network connectable along with one or more other computer systems to a network, the computer system including a processor and system memory, a method for creating an electronic message that can be sent using a plurality of different message protocols, that is formatted to be compatible with a plurality of different message applications, and that can be stored and accessed by any of the plurality of different message applications using any of the plurality of different messaging protocols, the method comprising: an act of the processor creating a single message item representing the electronic message in accordance with a general message schema, the single message item creation including: an act of defining one or more general data fields according to the general message schema that correspond to one or more general properties common to the plurality of different message protocols and common to the plurality of different message applications, including at least one data field corresponding to a primary type to the message item, the primary type indicating a primary behavior of a plurality of content portions linked to the message item; an act of formatting the single message item for compatibility with the plurality of different message protocols, including for each different message protocol in the plurality of different message protocols: an act of adding protocol specific data fields from at least one protocol specific extension schema to the single message item itself, to make the plurality of linked content portions compatible with the message protocol, each protocol specific extension schema accounting for any properties that are not common between the plurality of different message protocols; and an act of assigning values to the protocol specific data fields within the single message item; an act of formatting the single message item for compatibility with the plurality of different message applications, including for each different message application in the plurality of different message applications: an act of adding application specific data fields from at least one application specific extension schema to the message item itself, to make the plurality of linked content portions compatible with the message application, each application specific extension schema accounting for properties that are not common between the plurality of different message applications; and an act of assigning values to the application specific data fields within the single message item; an act of assigning values to one or more of the general data fields, thereby defining at least one general property that is common between two different extension schemas; and an act of sending the single message item, which has been formatted to include the protocol specific data fields for each of the plurality of different message protocols and the application specific data fields for each of the plurality of different message applications, to two or more of the plurality of different message applications via two or more of the plurality of different message protocols.