# Postmaster (computing)

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{{Short description|Administrator of an email server}}
In [electronic mail](/source/electronic_mail), a '''postmaster''' is the administrator of a [mail server](/source/mail_server). Nearly every domain should have an [e-mail address](/source/e-mail_address) like <code>postmaster@example.com</code> where errors in e-mail processing are directed. Error e-mails automatically generated by mail servers' [MTA](/source/Mail_transfer_agent)s usually appear to have been sent from the postmaster address.

Every domain that supports the [SMTP](/source/SMTP) protocol for electronic mail is required by [RFC](/source/Request_for_Comments) 5321<ref>{{harvnb|Klensin|2008|p=60}}</ref> and, as early as 1982, by RFC 822.<ref>{{Cite IETF
 |rfc=822
 |title=RFC 822 - STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES
 |editor-first=David H.
 |editor-last=Crocker
 |editor-link=Dave_Crocker_(engineer)
 |publisher=[IETF](/source/Internet_Engineering_Task_Force)
 |date=1982-08-13
 |access-date=2025-02-13
 |url=https://datatracker.ietf.org/doc/rfc822/
 |url-status=live
 |archive-url=https://web.archive.org/web/20250127102258/https://datatracker.ietf.org/doc/rfc822/
 |archive-date=2025-01-27
 |quote=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 />&nbsp;&nbsp;&nbsp;&nbsp;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.
}}</ref> Due to how common this address is across mail servers, it is a common target for spam.

== Specification ==
[RFC 5321](/source/rfc%3A5321), which defines the Simple Mail Transfer Protocol, specifies that all mail servers featuring the ability to [relay](/source/Open_mail_relay) or deliver email must have a "postmaster" mailbox, and that the postmaster should receive all mail sent to it in as much as possible (except, for example, in case of a [denial-of-service attack](/source/denial-of-service_attack)).<ref>{{harvnb|Klensin|2008|p=60}}</ref><ref name=':Costales473'>{{harvnb|Costales|Jansen|Assmann|2008|p=473}}</ref> Email send to the postmaster mailbox must also be received by a real person who's capable of handling issues with the mail server.<ref name=':Costales473'/>

Unless the mail server has a real account called "postmaster," the postmaster mailbox should be defined as an e-mail alias that expands to the address of a real user on the mail server.<ref name=':Costales473'/><ref name=':Costales13'>{{harvnb|Costales|Jansen|Assmann|2008|p=13}}</ref>

== Use ==
The purpose of the postmaster mailbox is to receive messages about issues with the mail server that hosts it.<ref>{{harvnb|Lucas|2024|p=58}}</ref> This mailbox follows the same pattern as the hostmaster and [webmaster](/source/webmaster) addresses, which are intended to receive DNS and web-related complaints respectively.<ref>{{harvnb|Costales|Jansen|Assmann|2008|p=298}}</ref>

For example, if email sent to another server is bounced, the receiving server may notify the sending server by sending a message to its postmaster.<ref>{{harvnb|Lucas|2024|p=246}}</ref> Mail programs are typically designed to notify the postmaster automatically when they detect problems, and users can also use this mailbox to notify the administrator of a mail server about issues on their own.<ref name=':Costales13' />

It is convention to send copies of bounced emails to the postmaster mailbox, however this is optional.<ref name=':Costales473'/> Sending the postmaster all bounced emails can pose privacy concerns for users, so some mail servers first pass all such messages through a filter to remove the e-mail's body, preserving only the headers to diagnose issues<ref >{{harvnb|Costales|Jansen|Assmann|2008|p=474}}</ref>

Since most domains have a postmaster address, it is commonly targeted by [spamming](/source/e-mail_spam) operations. Even if not directly spammed, a postmaster address may be sent [bounced](/source/bounce_message) spam from other servers that mistakenly trust fake [return-path](/source/return-path)s commonly used in spam.{{Citation needed|date=January 2026}}

==See also==
* [Webmaster](/source/Webmaster)
* [Moderator (communications)](/source/Moderator_(communications))
* [Forum administrator](/source/Forum_administrator)
* [Sysop](/source/Sysop)
* [Superuser](/source/Superuser)

==References==
<references/>

==Bibliography==
* {{Cite IETF
 |rfc=5321
 |title=RFC 5321 - Simple Mail Transfer Protocol
 |first=John C.
 |last=Klensin
 |author-link=John Klensin
 |publisher=[IETF](/source/Internet_Engineering_Task_Force)
 |date=October 2008
 |access-date=2025-02-13
 |url=https://datatracker.ietf.org/doc/rfc5321/
 |url-status=live
 |archive-url=https://web.archive.org/web/20250101215956/https://datatracker.ietf.org/doc/rfc5321/
 |archive-date=2025-01-01
}}
* {{cite book |last1=Lucas |first1=Michael |title=Run Your Own Mail Server |date=2024 |publisher=Tilted Windmill Press |isbn=978-1-64235-078-4}}
* {{cite book |last1=Costales |first1=Bryan |last2=Jansen |first2=George |last3=Assmann |first3=Claus |title=sendmail |date=2008 |publisher=O'Reilly Media |isbn=978-0-596-51029-9 |edition=4th}}

==External links==
* {{IETF RFC|5321|link=no}}: The SMTP Protocol

Category:Email

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Adapted from the Wikipedia article [Postmaster (computing)](https://en.wikipedia.org/wiki/Postmaster_(computing)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Postmaster_(computing)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.