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X-No-Archive is a newsgroup message header used to prevent a Usenet message from being archived in various servers.

It was designed to follow the standard message header protocol, RFC 1036 and 977, used in existing newsgroups. In addition to the standard message header lines used in all newsgroup messages (including Path:, From:, Subject:, and Date:), news reader software includes the option for a user to add additional, optional headers to messages. These additional headers are prefixed with the label X- so that they can be ignored by news servers and newsreaders. The phrase "No Archive" was coined as a way to state "Do not archive this message," and the X- header was added to complete the term X-No-Archive.

The proper header to prevent a message from being archived is as follows:

X-No-Archive: Yes

Some software systems also do not archive if the first line in the body of the message contains this text. This is useful for those users who cannot change the headers of messages they send out. If the X-No-Archive header is set to "No", or the header is absent, a Usenet archive will not recognise a prohibition on the message's archival.

Use of X-No-Archive began when DejaNews debuted in early 1995. DejaNews was the first large-scale, commercial attempt to archive the Usenet news feed, and a number of regular newsgroup participants were concerned about privacy rights, as well as the possibility that their messages could be re-posted through DejaNews at some point in the future. DejaNews addressed these concerns by announcing that it would not archive any Usenet messages containing the X-No-Archive header.

When DejaNews was purchased by Google, Google continued to honor the X-No-Archive protocol. Beginning in 2005, Google's newsgroup service (Google Groups) changed its handling of X-No-Archive, allowing messages with the header to be archived and made available for view for a period of six days; after six days, the message was then deleted from the archive. Other newsgroup archiving services have also followed in DejaNews' footsteps, though the decision not to archive X-No-Archive messages has been entirely voluntary.

Many popular newsreader and posting software programs, such as Forté Agent, include, as a standard option, the ability to insert an X-No-Archive header into any or all messages at the user's request.

Mozilla Thunderbird also has the ability to insert custom headers into both email and Usenet messages. This feature must be manually enabled by editing the mailnews.js file (instructions are included in the .js file). However, custom headers are not automatically inserted into messages by Thunderbird - the user must add them manually to each message as desired.