<s>
In	O
computers	O
and	O
technology	O
,	O
a	O
postmaster	B-General_Concept
is	O
the	O
administrator	O
of	O
a	O
mail	B-Protocol
server	I-Protocol
.	O
</s>
<s>
Nearly	O
every	O
domain	O
should	O
have	O
the	O
e-mail	O
address	O
postmaster@example.com	O
where	O
errors	O
in	O
e-mail	O
processing	O
are	O
directed	O
.	O
</s>
<s>
Error	O
e-mails	O
automatically	O
generated	O
by	O
mail	B-Protocol
servers	I-Protocol
 '	O
MTAs	O
usually	O
appear	O
to	O
have	O
been	O
sent	O
to	O
the	O
postmaster	B-General_Concept
address	O
.	O
</s>
<s>
Every	O
domain	O
that	O
supports	O
the	O
SMTP	B-Protocol
protocol	I-Protocol
for	O
electronic	O
mail	O
is	O
required	O
by	O
RFC	B-Protocol
5321	I-Protocol
and	O
,	O
as	O
early	O
as	O
1982	O
,	O
by	O
RFC	O
822	O
,	O
to	O
have	O
the	O
postmaster	B-General_Concept
address	O
.	O
</s>
<s>
Any	O
system	O
that	O
includes	O
an	O
SMTP	B-Protocol
server	I-Protocol
supporting	O
mail	O
relaying	O
or	O
delivery	O
MUST	O
support	O
the	O
reserved	O
mailbox	O
"	O
postmaster	B-General_Concept
"	O
as	O
a	O
case-insensitive	O
local	O
name	O
.	O
</s>
<s>
This	O
postmaster	B-General_Concept
address	O
is	O
not	O
strictly	O
necessary	O
if	O
the	O
server	O
always	O
returns	O
554	O
on	O
connection	O
opening	O
(	O
as	O
described	O
in	O
section	O
3.1	O
)	O
.In	O
the	O
case	O
of	O
a	O
connection-opening	O
response	O
,	O
554	O
means	O
"	O
No	O
SMTP	B-Protocol
service	O
here	O
"	O
,	O
and	O
may	O
contain	O
explanatory	O
information	O
.	O
</s>
<s>
The	O
requirement	O
to	O
accept	O
mail	O
for	O
postmaster	B-General_Concept
implies	O
that	O
RCPT	O
commands	O
which	O
specify	O
a	O
mailbox	O
for	O
postmaster	B-General_Concept
at	O
any	O
of	O
the	O
domains	O
for	O
which	O
the	O
SMTP	B-Protocol
server	I-Protocol
provides	O
mail	O
service	O
,	O
as	O
well	O
as	O
the	O
special	O
case	O
of	O
"	O
RCPT	O
TO:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1	O
"	O
(	O
with	O
no	O
domain	O
specification	O
)	O
,	O
MUST	O
be	O
supported	O
.	O
</s>
<s>
SMTP	B-Protocol
systems	O
are	O
expected	O
to	O
make	O
every	O
reasonable	O
effort	O
to	O
accept	O
mail	O
directed	O
to	O
Postmaster	B-General_Concept
from	O
any	O
other	O
system	O
on	O
the	O
Internet	O
.	O
</s>
<s>
In	O
extreme	O
cases	O
(	O
such	O
as	O
to	O
contain	O
a	O
denial	O
of	O
service	O
attack	O
or	O
other	O
breach	O
of	O
security	O
)	O
an	O
SMTP	B-Protocol
server	I-Protocol
may	O
block	O
mail	O
directed	O
to	O
Postmaster	B-General_Concept
.	O
</s>
<s>
Since	O
most	O
domains	O
have	O
a	O
postmaster	B-General_Concept
address	O
,	O
it	O
is	O
commonly	O
targeted	O
by	O
spamming	O
operations	O
.	O
</s>
<s>
Even	O
if	O
not	O
directly	O
spammed	O
,	O
a	O
postmaster	B-General_Concept
address	O
may	O
be	O
sent	O
bounced	O
spam	O
from	O
other	O
servers	O
that	O
mistakenly	O
trust	O
fake	O
return-paths	O
commonly	O
used	O
in	O
spam	O
.	O
</s>
