Unique ID Listing
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Unique ID Listing(messaging)
(UIDL) A system used by POP3 electronic mail servers to uniquely identify a mail message. Normally, a message is identified by its position in the list of messages but this will change when an earlier message is deleted. The UIDL is a fixed string of characters which is unique to the message. The UIDL of a message never changes and will never be reused, even when the message has been deleted from the user's mailbox.
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