Tracking Modified Messages

The PFRA maintains the following information about the state of each message in each folder.

• A monotonically increasing, information store-specific change number
• A list of predecessor change numbers (all previous change numbers for an information store)

The change number is made up of a unique identifier and a change counter, so the change numbers are information-store-specific.

The change counter is assigned a number by the PFRA for each message change that occurs on a server. When a message on an information store is modified, the PFRA for that information store assigns a new change number to the message so that the change counter is greater than the previous one.

By using the predecessor change number list, the PRFA tracks which version of a message is the most current.