<s>
MMDF	B-Application
,	O
the	O
Multichannel	O
Memorandum	O
Distribution	O
Facility	O
,	O
is	O
a	O
message	B-Protocol
transfer	I-Protocol
agent	I-Protocol
(	O
MTA	O
)	O
,	O
a	O
computer	O
program	O
designed	O
to	O
transmit	O
email	O
.	O
</s>
<s>
MMDF	B-Application
was	O
originally	O
developed	O
at	O
the	O
University	O
of	O
Delaware	O
in	O
the	O
late	O
1970s	O
,	O
and	O
provided	O
the	O
initial	O
means	O
of	O
operating	O
CSNET	O
,	O
the	O
predecessor	O
to	O
NSFNET	O
.	O
</s>
<s>
A	O
re-coded	O
variant	O
of	O
MMDF	B-Application
,	O
called	O
Pascal	B-Application
MDF	O
(	O
PMDF	O
)	O
was	O
written	O
at	O
the	O
University	O
of	O
Pennsylvania	O
for	O
VMS	B-Operating_System
and	O
was	O
eventually	O
commercialized	O
through	O
Ned	O
Freed	O
's	O
Innosoft	O
,	O
which	O
subsequently	O
ported	O
PMDF	O
to	O
Tru64	B-Operating_System
Unix	I-Operating_System
and	O
Solaris	B-Application
.	O
</s>
<s>
In	O
1999	O
PMDF	O
was	O
translated	O
from	O
Pascal	B-Application
to	O
C	B-Language
.	O
The	O
C	B-Language
version	O
of	O
PMDF	O
became	O
the	O
basis	O
of	O
the	O
Sun	B-Application
Java	I-Application
System	I-Application
Messaging	I-Application
Server	I-Application
of	O
Sun	O
Microsystems	O
,	O
while	O
rights	O
to	O
PMDF	O
itself	O
were	O
purchased	O
by	O
Process	O
Software	O
,	O
which	O
then	O
ported	O
PMDF	O
to	O
Linux	B-Application
.	O
</s>
<s>
As	O
its	O
name	O
denotes	O
,	O
MMDF	B-Application
is	O
an	O
MTA	O
oriented	O
around	O
the	O
idea	O
of	O
channels	O
.	O
</s>
<s>
This	O
makes	O
MMDF	B-Application
a	O
highly	O
modular	O
system	O
,	O
with	O
each	O
module	O
having	O
all	O
of	O
the	O
idiosyncratic	O
syntax	O
and	O
semantic	O
information	O
necessary	O
for	O
a	O
particular	O
email	O
technology	O
or	O
network	O
,	O
as	O
well	O
as	O
the	O
least	O
privilege	O
necessary	O
,	O
with	O
the	O
authority	O
of	O
each	O
module	O
partitioned	O
from	O
others	O
.	O
</s>
<s>
Internally	O
,	O
MMDF	B-Application
uses	O
a	O
canonical	B-General_Concept
representation	I-General_Concept
for	O
message	O
content	O
and	O
header	O
,	O
including	O
addresses	O
.	O
</s>
<s>
Some	O
examples	O
of	O
MMDF	B-Application
channels	O
are	O
SMTP	B-Protocol
,	O
UUCP	B-Protocol
,	O
and	O
local	O
(	O
for	O
delivering	O
mail	O
into	O
local	O
mailboxes	O
and	O
accepting	O
mail	O
submitted	O
on	O
the	O
local	O
system	O
)	O
.	O
</s>
<s>
MMDF	B-Application
was	O
used	O
on	O
the	O
CSNET	O
network	O
.	O
</s>
<s>
A	O
message	O
that	O
flows	O
through	O
MMDF	B-Application
will	O
typically	O
follow	O
this	O
path	O
:	O
</s>
<s>
It	O
invokes	O
the	O
core	O
of	O
the	O
MMDF	B-Application
system	O
,	O
a	O
program	O
called	O
submit	O
,	O
and	O
feeds	O
it	O
the	O
message	O
as	O
well	O
as	O
the	O
out-of-band	O
information	O
for	O
the	O
message	O
-	O
return	O
address	O
,	O
recipient	O
,	O
etc	O
.	O
</s>
<s>
MMDF	B-Application
approaches	O
administrative	O
configuration	O
differently	O
than	O
other	O
popular	O
MTAs	O
.	O
</s>
<s>
In	O
the	O
choice	O
between	O
placing	O
specialized	O
knowledge	O
into	O
the	O
software	O
,	O
versus	O
requiring	O
that	O
it	O
be	O
created	O
through	O
administrator	O
's	O
configuration	O
instructions	O
,	O
MMDF	B-Application
chose	O
the	O
former	O
.	O
</s>
<s>
Domain	O
tables	O
are	O
used	O
for	O
domain	O
name	O
canonicalization	B-General_Concept
.	O
</s>
<s>
Channel	O
tables	O
select	O
the	O
outbound	O
channel	O
on	O
the	O
basis	O
of	O
the	O
next-hop	O
domain	O
name	O
,	O
and	O
also	O
encode	O
per-domain-name	O
parameters	O
for	O
the	O
particular	O
channel	O
,	O
such	O
as	O
the	O
UUCP	B-Protocol
node	O
name	O
or	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
DNS	B-Protocol
can	O
be	O
and	O
usually	O
is	O
used	O
for	O
these	O
purposes	O
as	O
well	O
,	O
in	O
the	O
form	O
of	O
"	O
DNS	B-Protocol
tables	O
"	O
that	O
have	O
the	O
same	O
key-value	O
form	O
.	O
</s>
<s>
By	O
the	O
end	O
of	O
2006	O
,	O
MMDF	B-Application
had	O
a	O
market	O
share	O
well	O
behind	O
other	O
mailers	O
such	O
as	O
sendmail	B-Application
,	O
postfix	B-Application
,	O
qmail	B-Application
,	O
exim	B-Protocol
,	O
and	O
Microsoft	B-Operating_System
Exchange	I-Operating_System
.	O
</s>
<s>
MMDF	B-Application
is	O
considered	O
legacy	B-Device
software	I-Device
.	O
</s>
