Message-ID

{{Short description|Unique identifier for a digital message}}

Message-ID is a unique identifier for a digital message, most commonly a globally unique identifier used in email and Usenet newsgroups.{{cite book | title = Digital evidence and computer crime: forensic science, computers and the Internet | author = Eoghan Casey | publisher = Academic Press | year = 2004 | isbn = 0-12-163104-4 | page = 506 }}

Message-IDs are required to have a specific format which is a subset of an email address{{Cite journal|journal=RFC Series|url=https://www.rfc-editor.org/rfc/rfc5322|title=Internet Message Format|first=P.|last=Resnick|editor-first1=P |editor-last1=Resnick |date=October 4, 2008|via=www.rfc-editor.org|doi=10.17487/RFC5322|url-access=subscription}} 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|date=September 2016}}

Message-IDs, if present, are generated by the client program sending the email or by the first mail server.{{Cite journal|journal=RFC Series|url=https://www.rfc-editor.org/rfc/rfc5321|title=Simple Mail Transfer Protocol|first=J.|last=Klensin|date=October 4, 2008|via=www.rfc-editor.org|doi=10.17487/RFC5321|url-access=subscription}} A common method of generating such ID is by combining the time and domain name, for example: 950124.162336@example.com.{{Cite journal|journal=RFC Series|url=https://www.rfc-editor.org/rfc/rfc2392|title=Content-ID and Message-ID Uniform Resource Locators|first=E.|last=Levinson|date=August 4, 1998|via=www.rfc-editor.org|doi=10.17487/RFC2392|url-access=subscription}}