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<title>Postmaster (computing)</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Postmaster (computing)</span></span>

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<p>In <a href="Computers" class="mw-redirect" title="Computers">computers</a> and <a href="Technology" title="Technology">technology</a>, a <b>postmaster</b> is the administrator of a <a href="Mail_server" class="mw-redirect" title="Mail server">mail server</a>. Nearly every domain should have the <a href="E-mail_address" class="mw-redirect" title="E-mail address">e-mail address</a> postmaster@example.com where errors in <a href="Electronic_mail" class="mw-redirect" title="Electronic mail">e-mail</a> processing are directed. Error e-mails automatically generated by mail servers' <a href="Mail_transfer_agent" class="mw-redirect" title="Mail transfer agent">MTAs</a> usually appear to have been sent to the postmaster address.

</p><p>Every domain that supports the <a href="SMTP" class="mw-redirect" title="SMTP">SMTP</a> protocol for electronic mail is required by <a href="Request_for_Comments" title="Request for Comments">RFC</a> 5321<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> and, as early as 1982, by RFC 822,<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> to have the postmaster address.

Quoting from the RFC:

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<p>Any system that includes an SMTP server supporting mail relaying or delivery MUST support the reserved mailbox "postmaster" as a <a href="Case_sensitivity" title="Case sensitivity">case-insensitive</a> local name. This postmaster address is not strictly necessary if the server always returns 554 on connection opening (as described in section 3.1).<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The requirement to accept mail for postmaster implies that RCPT commands which specify a mailbox for postmaster at any of the domains for which the SMTP server provides mail service, as well as the special case of "RCPT TO:<Postmaster>" (with no domain specification), MUST be supported.

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<p>SMTP systems are expected to make every reasonable effort to accept mail directed to Postmaster from any other system on the Internet. In extreme cases (such as to contain a denial of service attack or other breach of security) an SMTP server may block mail directed to Postmaster. However, such arrangements SHOULD be narrowly tailored so as to avoid blocking messages which are not part of such attacks.

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<p>Since most domains have a postmaster address, it is commonly targeted by <a href="E-mail_spam" class="mw-redirect" title="E-mail spam">spamming</a> operations. Even if not directly spammed, a postmaster address may be sent <a href="Bounce_message" title="Bounce message">bounced</a> spam from other servers that mistakenly trust fake <a href="Return-path" class="mw-redirect" title="Return-path">return-paths</a> commonly used in spam.

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFKlensin2008" class="citation cs1"><a href="John_Klensin" title="John Klensin">Klensin, John C.</a> (October 2008). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/rfc5321/"><i>RFC 5321 - Simple Mail Transfer Protocol</i></a>. <a href="Internet_Engineering_Task_Force" title="Internet Engineering Task Force">IETF</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC5321">10.17487/RFC5321</a></span>. <a href="Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5321">5321</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20250101215956/https://datatracker.ietf.org/doc/rfc5321/">Archived</a> from the original on 2025-01-01<span class="reference-accessdate">. Retrieved <span class="nowrap">2025-02-13</span></span>.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFCrocker1982" class="citation cs1"><a href="Dave_Crocker_(engineer)" title="Dave Crocker (engineer)">Crocker, David H.</a>, ed. (1982-08-13). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/rfc822/"><i>RFC 822 - STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES</i></a>. <a href="Internet_Engineering_Task_Force" title="Internet Engineering Task Force">IETF</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC0822">10.17487/RFC0822</a></span>. <a href="Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc822">822</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20250127102258/https://datatracker.ietf.org/doc/rfc822/">Archived</a> from the original on 2025-01-27<span class="reference-accessdate">. Retrieved <span class="nowrap">2025-02-13</span></span>. <q>6.3. RESERVED ADDRESS<br>It often is necessary to send mail to a site, without knowing any of its valid addresses. For example, there may be mail system dysfunctions, or a user may wish to find out a person's correct address, at that site.<br><br>This standard specifies a single, reserved mailbox address (local-part) which is to be valid at each site. Mail sent to that address is to be routed to a person responsible for the site's mail system or to a person with responsibility for general site operation. The name of the reserved local-part address is:<br><br>    Postmaster<br><br>so that "Postmaster@domain" is required to be valid.<br><br>Note: This reserved local-part must be matched without sensitivity to alphabetic case, so that "POSTMASTER", "postmaster", and even "poStmASteR" is to be accepted.</q></cite></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">In the case of a connection-opening response, 554 means "No SMTP service here", and may contain explanatory information.</span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li>RFC <a rel="nofollow" class="external text" href="https://www.rfc-editor.org/rfc/rfc5321">5321</a>: The SMTP Protocol</li></ul>

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This article is issued from <a class="external text" title="Last edited on 2025-05-18" href="https://en.wikipedia.org/wiki/?title=Postmaster_(computing)&oldid=1290998731">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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