<s>
The	O
Local	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
LMTP	B-Protocol
)	O
is	O
an	O
alternative	O
to	O
(	O
Extended	O
)	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
for	O
situations	O
where	O
the	O
receiving	O
side	O
does	O
not	O
have	O
a	O
mail	O
queue	O
,	O
such	O
as	O
a	O
message	B-Protocol
transfer	I-Protocol
agent	I-Protocol
acting	O
as	O
a	O
message	B-Protocol
delivery	I-Protocol
agent	I-Protocol
.	O
</s>
<s>
LMTP	B-Protocol
was	O
described	O
in	O
in	O
1996	O
.	O
</s>
<s>
Mail	O
queues	O
are	O
an	O
inherent	O
requisite	O
of	O
SMTP	B-Protocol
.	O
</s>
<s>
In	O
situations	O
in	O
which	O
mail	O
queues	O
are	O
not	O
possible	O
,	O
LMTP	B-Protocol
is	O
desirable	O
,	O
since	O
a	O
mail	O
storage	O
server	O
should	O
manage	O
only	O
its	O
mail	O
store	O
without	O
having	O
to	O
allocate	O
more	O
storage	O
for	O
a	O
mail	O
queue	O
.	O
</s>
<s>
This	O
is	O
not	O
possible	O
with	O
SMTP	B-Protocol
when	O
there	O
are	O
multiple	O
recipients	O
for	O
a	O
mail	O
message	O
.	O
</s>
<s>
SMTP	B-Protocol
can	O
only	O
indicate	O
successful	O
delivery	O
or	O
failure	O
for	O
all	O
or	O
none	O
of	O
the	O
recipients	O
,	O
creating	O
the	O
need	O
for	O
a	O
separate	O
queue	O
to	O
handle	O
the	O
failed	O
recipients	O
.	O
</s>
<s>
LMTP	B-Protocol
,	O
on	O
the	O
other	O
hand	O
,	O
can	O
indicate	O
success	O
or	O
failure	O
to	O
the	O
client	O
for	O
each	O
recipient	O
,	O
allowing	O
the	O
client	O
to	O
handle	O
the	O
queueing	O
instead	O
.	O
</s>
<s>
LMTP	B-Protocol
is	O
not	O
intended	O
for	O
use	O
over	O
wide	O
area	O
networks	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
message	B-Protocol
transfer	I-Protocol
agent	I-Protocol
(	O
MTA	O
)	O
still	O
handles	O
all	O
outgoing	O
mail	O
,	O
including	O
the	O
mail	O
stream	O
from	O
the	O
LMTP	B-Protocol
,	O
to	O
another	O
mail	B-Protocol
server	I-Protocol
located	O
somewhere	O
on	O
the	O
Internet	O
.	O
</s>
<s>
LMTP	B-Protocol
is	O
an	O
Application	B-Application
Layer	I-Application
protocol	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
.	O
</s>
<s>
It	O
can	O
use	O
a	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
transport	O
like	O
SMTP	B-Protocol
,	O
but	O
must	O
not	O
use	O
port	B-Protocol
number	I-Protocol
25	O
,	O
the	O
well-known	O
port	O
for	O
SMTP	B-Protocol
.	O
</s>
<s>
Usage	O
of	O
port	O
24	O
(	O
"	O
any	O
private	O
mail	O
system	O
"	O
)	O
is	O
common	O
among	O
some	O
mail	B-Protocol
server	I-Protocol
applications	O
however	O
.	O
</s>
<s>
LMTP	B-Protocol
conversation	O
syntax	O
is	O
based	O
on	O
the	O
same	O
commands	O
as	O
SMTP	B-Protocol
(	O
formerly	O
called	O
Extended	B-Protocol
SMTP	I-Protocol
)	O
with	O
the	O
following	O
exceptions	O
:	O
</s>
<s>
ESMTP	B-Protocol
requires	O
a	O
single	O
status	O
for	O
the	O
entire	O
message	O
body	O
.	O
</s>
<s>
LMTP	B-Protocol
requires	O
a	O
response	O
for	O
each	O
previously	O
successful	O
RCPT	O
command	O
.	O
</s>
<s>
That	O
is	O
,	O
in	O
case	O
of	O
multiple	O
recipients	O
,	O
after	O
the	O
body	O
of	O
the	O
message	O
has	O
been	O
transmitted	O
,	O
LMTP	B-Protocol
can	O
still	O
fail	O
for	O
some	O
recipient	O
while	O
succeeding	O
for	O
the	O
others	O
.	O
</s>
<s>
With	O
this	O
facility	O
,	O
LMTP	B-Protocol
can	O
fail	O
if	O
a	O
user	O
is	O
over	O
quota	O
without	O
the	O
burden	O
of	O
generating	O
bounce	O
messages	O
.	O
</s>
<s>
The	O
key	O
difference	O
is	O
that	O
LMTP	B-Protocol
will	O
reject	O
a	O
message	O
for	O
a	O
specific	O
final	O
recipient	O
if	O
it	O
is	O
not	O
immediately	O
deliverable	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
LMTP	B-Protocol
is	O
not	O
run	O
on	O
the	O
standard	O
TCP	B-Protocol
port	I-Protocol
of	O
SMTP	B-Protocol
.	O
</s>
