Search notes:

Outlook Object Model: MailItem.EntryId

mailItem.entryId is a string whose value is a MailItem's unique ID which identifies a MailItem.
This value can be used to find a specific mail item, for example to display it: 
dim ns as namespace
set ns = application.getNamespace("MAPI")

dim msg as mailItem
set msg = ns.getItemFromId("0000.....ABCC...")

msg.display

See also

This property corresponds to the MAPI property pidTagEntryId.

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