<s>
qpsmtpd	B-Language
is	O
an	O
SMTP	B-Protocol
daemon	B-Operating_System
written	O
in	O
Perl	B-Language
.	O
</s>
<s>
It	O
was	O
originally	O
designed	O
to	O
be	O
a	O
drop-in	O
replacement	O
for	O
qmail-smtpd	O
,	O
the	O
SMTP	B-Protocol
component	O
of	O
qmail	B-Application
,	O
and	O
it	O
is	O
now	O
also	O
compatible	O
with	O
Postfix	B-Application
,	O
Exim	B-Protocol
,	O
sendmail	B-Application
and	O
virtually	O
any	O
software	O
that	O
"	O
speaks	O
SMTP	B-Protocol
"	O
.	O
</s>
<s>
Its	O
main	O
purpose	O
is	O
to	O
allow	O
mail	O
administrators	O
to	O
perform	O
more	O
advanced	O
spam	O
filtering	O
than	O
is	O
possible	O
with	O
other	O
SMTP	B-Protocol
daemons	B-Operating_System
.	O
</s>
<s>
As	O
one	O
example	O
of	O
dozens	O
,	O
the	O
earlytalker	O
plugin	O
blocks	O
many	O
viruses	O
and	O
mass	O
mailers	O
based	O
on	O
their	O
characteristic	O
violation	O
of	O
basic	O
protocol	B-Protocol
,	O
even	O
before	O
they	O
start	O
sending	O
mail	O
data	O
.	O
</s>
<s>
It	O
is	O
licensed	O
under	O
the	B-License
MIT	I-License
License	I-License
.	O
</s>
<s>
A	O
defining	O
virtue	O
of	O
qpsmtpd	B-Language
is	O
its	O
plugin	O
system	O
and	O
collection	O
of	O
plugins	O
.	O
</s>
<s>
In	O
addition	O
to	O
basic	O
plugins	O
qpsmtpd	B-Language
has	O
a	O
suite	O
of	O
additional	O
plugins	O
that	O
provide	O
integration	O
with	O
external	O
mail	O
filters	O
and	O
processors	O
as	O
well	O
as	O
implementations	O
of	O
many	O
email	O
technologies	O
.	O
</s>
<s>
The	O
following	O
list	O
is	O
just	O
a	O
few	O
of	O
the	O
many	O
qpsmtpd	B-Language
plugins	O
.	O
</s>
<s>
Name	O
Description	O
GeoIP	B-Application
Use	O
GeoIP	B-Application
databases	O
to	O
report	O
geographic	O
information	O
about	O
incoming	O
connections	O
,	O
including	O
distance	O
in	O
km	O
.	O
</s>
<s>
p0f	B-Protocol
p0f	B-Protocol
uses	O
TCP	O
fingerprint	O
info	O
to	O
identify	O
the	O
senders	O
Operating	O
System	O
,	O
network	O
distance	O
,	O
and	O
more	O
.	O
</s>
<s>
dnsbl	O
DNS	O
blacklists	O
earlytalker	O
Assure	O
the	O
client	O
does	O
n't	O
talk	O
before	O
we	O
send	O
the	O
SMTP	B-Protocol
banner	O
helo	O
validate	O
the	O
HELO	O
or	O
EHLO	B-Protocol
message	O
presented	O
by	O
the	O
sender	O
auth:*	O
plugins	O
for	O
user	O
authentication	O
include	O
vpopmail	O
,	O
checkpassword	O
,	O
flat_file	O
,	O
and	O
ldap	O
SPF	O
Sender	B-Protocol
Policy	I-Protocol
Framework	I-Protocol
greylisting	O
temporary	O
deferrals	O
for	O
unknown	O
senders	O
headers	O
message	O
header	O
validation	O
URIBL	O
scan	O
message	O
content	O
for	O
blacklisted	O
URLs	O
Domainkeys	B-Protocol
validate	O
domainkeys	B-Protocol
signatures	I-Protocol
on	O
incoming	O
mail	O
DKIM	B-Protocol
validate	O
DKIM	B-Protocol
signatures	O
and	O
DKIM	B-Protocol
sign	O
outgoing	O
messages	O
DMARC	O
implements	O
the	O
draft	O
DMARC	O
specification	O
for	O
email	O
authentication	O
SpamAssassin	B-Language
the	O
venerable	O
spam	O
detector	O
dspam	O
DSPAM	O
is	O
a	O
bayesian	O
anti-spam	O
filter	O
optimized	O
for	O
speed	O
.	O
</s>
