<s>
A	O
message	B-Protocol
delivery	I-Protocol
agent	I-Protocol
(	O
MDA	O
)	O
,	O
or	O
mail	B-Protocol
delivery	I-Protocol
agent	I-Protocol
,	O
is	O
a	O
computer	O
software	O
component	O
that	O
is	O
responsible	O
for	O
the	O
delivery	O
of	O
e-mail	O
messages	O
to	O
a	O
local	O
recipient	O
's	O
mailbox	O
.	O
</s>
<s>
It	O
is	O
also	O
called	O
a	O
local	B-Protocol
delivery	I-Protocol
agent	I-Protocol
(	O
LDA	O
)	O
.	O
</s>
<s>
Within	O
the	O
Internet	O
mail	O
architecture	O
,	O
local	O
message	O
delivery	O
is	O
achieved	O
through	O
a	O
process	O
of	O
handling	O
messages	O
from	O
the	O
message	B-Protocol
transfer	I-Protocol
agent	I-Protocol
,	O
and	O
storing	O
mail	O
into	O
the	O
recipient	O
's	O
environment	O
(	O
typically	O
a	O
mailbox	O
)	O
.	O
</s>
<s>
Many	O
mail	O
handling	O
software	O
products	O
bundle	O
multiple	O
message	B-Protocol
delivery	I-Protocol
agents	I-Protocol
with	O
the	O
message	B-Protocol
transfer	I-Protocol
agent	I-Protocol
component	O
,	O
providing	O
for	O
site	O
customization	O
of	O
the	O
specifics	O
of	O
mail	O
delivery	O
to	O
a	O
user	O
.	O
</s>
<s>
On	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
procmail	B-Protocol
and	O
maildrop	B-Protocol
are	O
the	O
most	O
popular	O
MDAs	O
.	O
</s>
<s>
The	O
Local	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
LMTP	B-Protocol
)	O
is	O
a	O
protocol	O
that	O
is	O
frequently	O
implemented	O
by	O
network-aware	O
MDAs	O
.	O
</s>
<s>
The	O
mail	B-Protocol
delivery	I-Protocol
agent	I-Protocol
is	O
generally	O
not	O
started	O
from	O
the	O
command	O
line	O
,	O
but	O
is	O
usually	O
invoked	O
by	O
mail	O
delivery	O
subsystems	O
,	O
such	O
as	O
a	O
mail	B-Protocol
transport	I-Protocol
agent	I-Protocol
,	O
or	O
a	O
mail	B-Protocol
retrieval	I-Protocol
agent	I-Protocol
.	O
</s>
