<s>
MXlo	B-Protocol
means	O
DNS	B-Protocol
resource	O
records	O
of	O
the	O
MX	B-Protocol
type	O
that	O
have	O
a	O
value	O
of	O
localhost	B-Protocol
.	O
</s>
<s>
The	O
name	O
comes	O
from	O
combining	O
the	O
MX	B-Protocol
from	O
Mail	O
eXchange	O
and	O
the	O
lo	O
abbreviation	O
for	O
a	O
loopback	B-Protocol
networking	O
interface	O
,	O
and	O
is	O
an	O
anti-spam	O
technique	O
that	O
is	O
growing	O
in	O
popularity	O
with	O
network	O
administrators	O
who	O
manage	O
a	O
large	O
number	O
of	O
unused	O
legacy	O
domain	O
names	O
.	O
</s>
<s>
MX	B-Protocol
records	I-Protocol
provide	O
a	O
resource	O
for	O
internet	B-Device
hosts	I-Device
to	O
discover	O
the	O
designated	O
SMTP	B-Protocol
service	O
for	O
a	O
given	O
domain	O
.	O
</s>
<s>
By	O
pointing	O
MX	B-Protocol
records	I-Protocol
for	O
unused	O
domains	O
to	O
localhost/127.0.0.1	O
,	O
any	O
SMTP	B-Protocol
traffic	O
to	O
these	O
domains	O
is	O
sent	O
back	O
to	O
the	O
originating	O
host	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
unused	O
domains	O
,	O
particularly	O
those	O
that	O
have	O
been	O
actively	O
used	O
and	O
receive	O
large	O
amounts	O
of	O
spam	O
,	O
this	O
practice	O
places	O
the	O
system	B-Operating_System
load	I-Operating_System
on	O
the	O
originating	O
server	B-Application
.	O
</s>
<s>
MXlo	B-Protocol
was	O
conceived	O
by	O
a	O
lone	O
network	O
administrator	O
for	O
a	O
large	O
engineering	O
corporation	O
.	O
</s>
<s>
As	O
the	O
company	O
acquired	O
and	O
subsequently	O
retired	O
domain	O
names	O
,	O
the	O
MX	B-Protocol
records	I-Protocol
for	O
these	O
domains	O
were	O
pointed	O
to	O
localhost	B-Protocol
to	O
minimize	O
system	B-Operating_System
load	I-Operating_System
from	O
unwanted	O
traffic	O
.	O
</s>
<s>
As	O
admins	O
and	O
other	O
technical	O
people	O
described	O
this	O
practice	O
to	O
each	O
other	O
,	O
it	O
picked	O
up	O
the	O
nickname	O
MXlo	B-Protocol
.	O
</s>
<s>
For	O
systems	O
and	O
providers	O
that	O
transmit	O
a	O
large	O
volume	O
of	O
spam	O
,	O
sufficient	O
use	O
of	O
the	O
MXlo	B-Protocol
practice	O
can	O
cause	O
a	O
self-inflicted	O
DoS	O
(	O
denial	O
of	O
service	O
)	O
attack	O
,	O
motivating	O
the	O
affected	O
provider	O
to	O
prevent	O
the	O
sending	O
of	O
spam	O
through	O
their	O
systems	O
.	O
</s>
<s>
IN	O
MX	B-Protocol
10	O
localhost	B-Protocol
.	O
</s>
<s>
A	O
practice	O
that	O
has	O
grown	O
with	O
the	O
MXlo	B-Protocol
concept	O
is	O
seeding	O
.	O
</s>
<s>
Once	O
MXlo	B-Protocol
has	O
been	O
implemented	O
for	O
a	O
given	O
domain	O
,	O
and	O
if	O
there	O
is	O
no	O
intention	O
to	O
use	O
the	O
domain	O
anymore	O
,	O
some	O
administrators	O
seed	O
spam	O
lists	O
by	O
publishing	O
fake	O
e-mail	O
addresses	O
associated	O
with	O
the	O
target	O
domain	O
in	O
public	O
forums	O
—	O
blogs	O
,	O
wiki	O
sites	O
,	O
etc.	O
—	O
and	O
entering	O
them	O
in	O
web	O
forms	O
that	O
spammers	O
are	O
known	O
to	O
harvest	O
e-mail	O
addresses	O
from	O
.	O
</s>
<s>
This	O
technique	O
intentionally	O
creates	O
unnecessary	O
traffic	O
for	O
high	O
volume	O
spam	O
hosts	B-Device
and	O
increases	O
their	O
operating	O
costs	O
—	O
and	O
,	O
in	O
some	O
cases	O
,	O
assists	O
the	O
aforementioned	O
self-inflicted	O
DoS	O
attacks	O
.	O
</s>
