<s>
Maildrop	B-Protocol
is	O
a	O
Mail	B-Protocol
delivery	I-Protocol
agent	I-Protocol
used	O
by	O
the	O
Courier	B-Protocol
Mail	I-Protocol
Server	I-Protocol
.	O
</s>
<s>
The	O
maildrop	B-Protocol
Mail	B-Protocol
Delivery	I-Protocol
Agent	I-Protocol
(	O
MDA	O
)	O
also	O
includes	O
filtering	O
functionality	O
.	O
</s>
<s>
Maildrop	B-Protocol
receives	O
mail	O
via	O
stdin	O
and	O
delivers	O
in	O
both	O
Maildir	O
and	O
mbox	B-Application
formats	O
.	O
</s>
<s>
Maildrop	B-Protocol
can	O
optionally	O
read	O
filtering	O
configuration	O
from	O
a	O
file	O
to	O
determine	O
whether	O
the	O
message	O
is	O
delivered	O
to	O
an	O
alternate	O
mailbox	O
or	O
forwarded	O
.	O
</s>
<s>
The	O
structured	O
filtering	O
language	O
is	O
robust	O
enough	O
to	O
allow	O
maildrop	B-Protocol
to	O
work	O
with	O
virtual	O
mailboxes	O
.	O
</s>
<s>
If	O
the	O
filtering	O
configuration	O
contains	O
syntax	O
errors	O
maildrop	B-Protocol
does	O
not	O
deliver	O
the	O
message	O
but	O
the	O
message	O
is	O
not	O
lost	O
.	O
</s>
<s>
Maildrop	B-Protocol
can	O
run	O
in	O
different	O
modes	O
,	O
depending	O
on	O
the	O
calling	O
environment	O
.	O
</s>
<s>
Delivery	O
mode	O
is	O
the	O
"	O
normal	O
"	O
mail	O
filtering	O
mode	O
;	O
that	O
is	O
,	O
during	O
final	O
delivery	O
,	O
after	O
the	O
message	O
left	O
the	O
SMTP	B-Protocol
environment	O
.	O
</s>
<s>
However	O
,	O
maildrop	B-Protocol
can	O
also	O
run	O
in	O
embedded	O
mode	O
;	O
that	O
is	O
,	O
during	O
an	O
SMTP	B-Protocol
transaction	O
.	O
</s>
<s>
Finally	O
,	O
maildrop	B-Protocol
can	O
run	O
in	O
manual	O
mode	O
,	O
like	O
any	O
other	O
interpreter	B-Application
.	O
</s>
<s>
Maildrop	B-Protocol
is	O
written	O
in	O
C++	O
.	O
</s>
<s>
However	O
,	O
it	O
uses	O
resources	O
more	O
efficiently	O
than	O
procmail	B-Protocol
(	O
written	O
in	O
C	O
)	O
by	O
saving	O
large	O
messages	O
to	O
a	O
temporary	O
file	O
rather	O
than	O
reading	O
them	O
into	O
memory	O
.	O
</s>
<s>
If	O
the	O
input	O
to	O
maildrop	B-Protocol
is	O
a	O
file	O
then	O
a	O
temporary	O
file	O
is	O
not	O
used	O
.	O
</s>
