Message-ID - AbsoluteAstronomy.com

Message-ID is a unique identifier

Unique identifier

With reference to a given set of objects, a unique identifier is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose...

for a digital message

Message

A message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form...

, most commonly a globally unique identifier

Globally Unique Identifier

A globally unique identifier is a unique reference number used as an identifier in computer software. The term GUID also is used for Microsoft's implementation of the Universally unique identifier standard....

used in email

Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

and Usenet newsgroups.

Message-IDs are required to have a specific format which is a subset of an email address (though Microsoft Outlook

Microsoft Outlook

Microsoft Outlook is a personal information manager from Microsoft, available both as a separate application as well as a part of the Microsoft Office suite...

is known to generate invalid IDs with three parts) and to be globally unique. That is, no two different messages must ever have the same Message-ID. A common technique used by many message systems is to use a time and date stamp along with the local host's domain name, e.g., 950124.162336@example.com.

See also