Message-ID is a
unique identifier
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 ...
for a digital message, most commonly a
globally unique identifier used in
email
Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" mean ...
and
Usenet newsgroup
A Usenet newsgroup is a repository usually within the Usenet system, for messages posted from users in different locations using the Internet. They are discussion groups and are not devoted to publishing news. Newsgroups are technically distin ...
s.
Message-IDs are required to have a specific format which is a subset of an
email address
An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineer ...
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.
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 is by combining the time and domain name, for example: 950124.162336@example.com.
References
{{reflist
External links
Recommendations for generating Message IDsMessageID-Finder Thunderbird extensionThunderLink Thunderbird extension
Unique identifiers
Email
Usenet