MAIL SYSTEM SYNCHRONIZATION USING MULTIPLE MESSAGE IDENTIFIERS

An electronic mail system includes multiple devices, on each of which a user may have an electronic mailbox. The electronic mailboxes can be synchronized, so that actions taken on one device are reflected on other devices. Each mail message is assigned a unique message identifier. When the message is read or moved from one folder to another folder, it is assigned a new message identifier. The system maintains a list of subsidiary identifiers for each message, which identifies the prior message identifiers for the message. The system identifies message identifiers that have been added since the last synchronization. During synchronization, by examining messages having a current or prior message identifier that is found in the list of subsidiary identifiers for a message having a new message identifier, the system is able to synchronize the mailboxes on the devices. Following synchronization, each synchronized device will have the same messages in the same folders, with the same message identifiers, and duplicates caused by taking the same action on two different devices are removed.