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Message-ID is a unique identifier for a digital message, most commonly a globally unique identifier used in email and Usenet newsgroups.[1]

Message-IDs are required to have a specific format which is a subset of an email address[2] 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 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.[citation needed]

Message-IDs, if present, are generated by the client program sending the email[3] or by the first mail server.[4] A common method of generating such ID is by combining the time and domain name, for example:[5]

Use in mailing list archives[edit]

Mails to public mailing-lists and news groups can be found via their Message-ID by using links from various services:<>$1jlj$;msgid=01041316021102.03716%40localhost.localdomain

See also[edit]


  1. ^ Eoghan Casey (2004). Digital evidence and computer crime: forensic science, computers and the Internet. Academic Press. p. 506. ISBN 0-12-163104-4.
  2. ^ RFC5322 – Internet Message Format
  3. ^ RFC5322 – Internet Message Format
  4. ^ RFC5321 – Simple Mail Transfer Protocol
  5. ^ RFC2392 – Content-ID and Message-ID Uniform Resource Locators