3.3.4.3.3.2.1.2 Avoiding Duplicate Uploads

When a client that is using a local replica sends a message by using a server with a major version of less than eight (8), a new message is created in a server folder, the contents of the local message are copied into the server message, and the message is submitted (on the first upload). After the submission is complete, the item is moved into the Sent Items folder in the local replica. Sometime later, the Sent Items folder is synchronized. The item is then uploaded as it is a new item in the replica (on the second upload) due to the fact that the folder to which the message was originally submitted is not within the user's mailbox (and therefore not part of the replica).

Servers with a major version of 8 and above implement the following alternative method to diminish the impact of the second upload. For details about determining server version, see section 1.7. Because the client assigns server IDs to all items it creates in the local replica, the message in the Outbox folder has a valid server ID. When the client is uploading the message for sending, it adds an additional property to the message, PidTagTargetEntryId ([MS-OXOMSG] section 2.2.1.76). When a version 8 (or later) server observes this property, it places a mirror copy of the message in the user's server Outbox and gives it the ID specified in the PidTagTargetEntryId property. In this way, when the client synchronizes the folder holding sent items, it can be synchronized as a move (from the Outbox folder to the folder holding sent items) as opposed to a new item (in the folder holding sent items).