<s>
Sendmail	B-Application
is	O
a	O
general	O
purpose	O
internetwork	B-Architecture
email	O
routing	O
facility	O
that	O
supports	O
many	O
kinds	O
of	O
mail-transfer	O
and	O
delivery	O
methods	O
,	O
including	O
the	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
used	O
for	O
email	O
transport	O
over	O
the	O
Internet	O
.	O
</s>
<s>
A	O
descendant	O
of	O
the	O
delivermail	B-Protocol
program	O
written	O
by	O
Eric	O
Allman	O
,	O
Sendmail	B-Application
is	O
a	O
well-known	O
project	O
of	O
the	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
and	O
Unix	B-Application
communities	O
.	O
</s>
<s>
It	O
has	O
spread	O
both	O
as	O
free	B-Application
software	I-Application
and	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
Allman	O
had	O
written	O
the	O
original	O
ARPANET	O
delivermail	B-Protocol
which	O
shipped	O
in	O
1979	O
with	O
4.0	O
and	O
4.1	O
BSD	B-Operating_System
.	O
</s>
<s>
He	O
wrote	O
Sendmail	B-Application
as	O
a	O
derivative	O
of	O
delivermail	B-Protocol
in	O
the	O
early	O
1980s	O
at	O
UC	O
Berkeley	O
.	O
</s>
<s>
It	O
shipped	O
with	O
BSD	B-Operating_System
4.1c	O
in	O
1983	O
,	O
the	O
first	O
BSD	B-Operating_System
version	O
that	O
included	O
TCP/IP	O
protocols	O
.	O
</s>
<s>
In	O
1996	O
,	O
approximately	O
80%	O
of	O
the	O
publicly	O
reachable	O
mail-servers	O
on	O
the	O
Internet	O
ran	O
Sendmail	B-Application
.	O
</s>
<s>
More	O
recent	O
surveys	O
have	O
suggested	O
a	O
decline	O
,	O
with	O
3.64	O
%	O
of	O
mail	B-Protocol
servers	I-Protocol
in	O
March	O
2021	O
detected	O
as	O
running	O
Sendmail	B-Application
in	O
a	O
study	O
performed	O
by	O
E-Soft	O
,	O
Inc	O
.	O
A	O
previous	O
survey	O
(	O
December	O
2007	O
or	O
earlier	O
)	O
reported	O
24%	O
of	O
mail	B-Protocol
servers	I-Protocol
running	O
Sendmail	B-Application
according	O
to	O
a	O
study	O
performed	O
by	O
Mail	O
Radar	O
.	O
</s>
<s>
Allman	O
designed	O
Sendmail	B-Application
to	O
incorporate	O
great	O
flexibility	O
,	O
but	O
it	O
can	O
be	O
daunting	O
to	O
configure	O
for	O
novices	O
.	O
</s>
<s>
Standard	O
configuration	O
packages	O
delivered	O
with	O
the	O
source	O
code	O
distribution	O
require	O
the	O
use	O
of	O
the	O
M4	B-Device
macro	I-Device
language	I-Device
which	O
hides	O
much	O
of	O
the	O
configuration	O
complexity	O
.	O
</s>
<s>
Sendmail	B-Application
supports	O
a	O
variety	O
of	O
mail	O
transfer	B-Protocol
protocols	I-Protocol
,	O
including	O
SMTP	B-Protocol
,	O
DECnet	B-Protocol
's	O
Mail-11	O
,	O
HylaFax	O
,	O
QuickPage	O
and	O
UUCP	B-Protocol
.	O
</s>
<s>
Additionally	O
,	O
Sendmail	B-Application
v8.12	O
introduced	O
support	O
for	O
milters	B-Application
-	O
external	O
mail	O
filtering	O
programs	O
that	O
can	O
participate	O
in	O
each	O
step	O
of	O
the	O
SMTP	B-Protocol
conversation	O
.	O
</s>
<s>
Sendmail	B-Application
,	O
Inc	O
was	O
acquired	O
by	O
Proofpoint	O
,	O
Inc	O
.	O
</s>
<s>
Sendmail	B-Application
originated	O
in	O
the	O
early	O
days	O
of	O
the	O
Internet	O
,	O
an	O
era	O
when	O
considerations	O
of	O
security	O
did	O
not	O
play	O
a	O
primary	O
role	O
in	O
the	O
development	O
of	O
network	O
software	O
.	O
</s>
<s>
Early	O
versions	O
of	O
Sendmail	B-Application
suffered	O
from	O
a	O
number	O
of	O
security	O
vulnerabilities	O
that	O
have	O
been	O
corrected	O
over	O
the	O
years	O
.	O
</s>
<s>
Sendmail	B-Application
itself	O
incorporated	O
a	O
certain	O
amount	O
of	O
privilege	O
separation	O
in	O
order	O
to	O
avoid	O
exposure	O
to	O
security	O
issues	O
.	O
</s>
<s>
,	O
current	O
versions	O
of	O
Sendmail	B-Application
,	O
like	O
other	O
modern	O
MTAs	B-Protocol
,	O
incorporate	O
a	O
number	O
of	O
security	O
improvements	O
and	O
optional	O
features	O
that	O
can	O
be	O
configured	O
to	O
improve	O
security	O
and	O
help	O
prevent	O
abuse	O
.	O
</s>
<s>
Sendmail	B-Application
vulnerabilities	O
in	O
CERT	O
advisories	O
and	O
alerts	O
:	O
</s>
<s>
The	O
UNIX-HATERS	O
Handbook	O
dedicated	O
an	O
entire	O
chapter	O
to	O
perceived	O
problems	O
and	O
weaknesses	O
of	O
sendmail	B-Application
.	O
</s>
<s>
As	O
of	O
sendmail	B-Application
release	O
8.12.0	O
the	O
default	O
implementation	O
of	O
sendmail	B-Application
runs	O
as	O
the	O
Unix	B-Application
user	O
smmsp	O
—	O
the	O
sendmail	B-Application
message	O
submission	O
program	O
.	O
</s>
