computers A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs ...

and

technology Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, science, ...

, a postmaster is the administrator of a

mail server Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host ...

. Nearly every domain should have the

e-mail 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 ...

postmaster@example.com where errors in

e-mail 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" meant ...

processing are directed. Error e-mails automatically generated by mail servers' MTAs usually appear to have been sent to the postmaster address. Every domain that supports the

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typical ...

protocol for electronic mail is required by RFC 5321 and, as early as 1982, by RFC 822, to have the postmaster address. The rfc-ignorant.org website used to maintain a list of domains that do not comply with the RFC based on this requirement, but was shut down in November 2012. The websit
RFC² Realtime List
expanded to include rfc-ignorant's lists after they shut down. Quoting from the RFC:

Any system that includes an SMTP server supporting mail relaying or delivery MUST support the reserved mailbox "postmaster" as a
case-insensitive In computers, case sensitivity defines whether uppercase and lowercase letters are treated as distinct (case-sensitive) or equivalent (case-insensitive). For instance, when users interested in learning about dogs search an e-book, "dog" and "Dog" 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).In the case of a connection-opening response, 554 means "No SMTP service here", and may contain explanatory information. 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:" (with no domain specification), MUST be supported.

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.

Since most domains have a postmaster address, it is commonly targeted by

spamming Spamming is the use of messaging systems to send multiple unsolicited messages (spam) to large numbers of recipients for the purpose of commercial advertising, for the purpose of non-commercial proselytizing, for any prohibited purpose (especial ...

operations. Even if not directly spammed, a postmaster address may be sent bounced spam from other servers that mistakenly trust fake return-paths commonly used in spam.

References

External links

* RFC 5321: The SMTP Protocol Email {{Compu-stub