A unique identifier ( UID ) is an identifier that is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. The concept was formalized early in the development of computer science and information systems . In general, it was associated with an atomic data type .
4-414: Message-ID is a unique identifier for a digital message, most commonly a globally unique identifier used in email and Usenet newsgroups . Message-IDs are required to have a specific format which is a subset of an email address and be globally unique. No two different messages must ever have the same Message-ID. If two messages have the same Message-ID, they are assumed to be the same and one version
8-457: A different generation strategy: The above methods can be combined, hierarchically or singly, to create other generation schemes which guarantee uniqueness. In many cases, a single object may have more than one unique identifier, each of which identifies it for a different purpose. National identification number is used by the governments of many countries as a means of tracking their citizens , permanent residents , and temporary residents for
12-403: Is by combining the time and domain name, for example: 950124.162336@example.com. Unique identifier In relational databases , certain attributes of an entity that serve as unique identifiers are called primary keys . In mathematics, set theory uses the concept of element indices as unique identifiers. There are some main types of unique identifiers, each corresponding to
16-446: Is discarded. This can cause issues if tools mangle the IDs created by other tools. Such a problem has been reported with Google MTAs mangling Message-IDs created by Outlook, making it difficult to reference other messages and breaking threading. Message-IDs, if present, are generated by the client program sending the email or by the first mail server . A common method of generating such ID
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