<s>
Microsoft	O
Exchange	O
Server	O
is	O
a	O
mail	B-Protocol
server	I-Protocol
and	O
calendaring	B-Application
server	O
developed	O
by	O
Microsoft	O
.	O
</s>
<s>
It	O
runs	O
exclusively	O
on	O
Windows	B-Device
Server	I-Device
operating	O
systems	O
.	O
</s>
<s>
The	O
first	O
version	O
was	O
called	O
Exchange	O
Server	O
4.0	O
,	O
to	O
position	O
it	O
as	O
the	O
successor	O
to	O
the	O
related	O
Microsoft	B-Application
Mail	I-Application
3.5	O
.	O
</s>
<s>
Exchange	O
initially	O
used	O
the	O
X.400	B-Protocol
directory	O
service	O
but	O
switched	O
to	O
Active	B-Protocol
Directory	I-Protocol
later	O
.	O
</s>
<s>
Until	O
version	O
5.0	O
,	O
it	O
came	O
bundled	O
with	O
an	O
email	B-Protocol
client	I-Protocol
called	O
Microsoft	B-Application
Exchange	I-Application
Client	I-Application
.	O
</s>
<s>
This	O
was	O
discontinued	O
in	O
favor	O
of	O
Microsoft	B-Application
Outlook	I-Application
.	O
</s>
<s>
Exchange	O
Server	O
primarily	O
uses	O
a	O
proprietary	B-Application
protocol	O
called	O
MAPI	B-Protocol
to	O
talk	O
to	O
email	B-Protocol
clients	I-Protocol
,	O
but	O
subsequently	O
added	O
support	O
for	O
POP3	B-Protocol
,	O
IMAP	B-Protocol
,	O
and	O
EAS	B-Protocol
.	O
</s>
<s>
The	O
standard	O
SMTP	B-Protocol
protocol	I-Protocol
is	O
used	O
to	O
communicate	O
to	O
other	O
Internet	O
mail	B-Protocol
servers	I-Protocol
.	O
</s>
<s>
Exchange	O
Server	O
is	O
licensed	O
both	O
as	O
on-premises	B-General_Concept
software	I-General_Concept
and	O
software	B-Architecture
as	I-Architecture
a	I-Architecture
service	I-Architecture
(	O
SaaS	B-Architecture
)	O
.	O
</s>
<s>
In	O
the	O
on-premises	B-General_Concept
form	O
,	O
customers	O
purchase	O
client	B-License
access	I-License
licenses	I-License
(	O
CALs	O
)	O
;	O
as	O
SaaS	B-Architecture
,	O
Microsoft	O
charges	O
a	O
monthly	O
service	O
fee	O
instead	O
.	O
</s>
<s>
Microsoft	O
had	O
sold	O
a	O
number	O
of	O
simpler	O
email	O
products	O
before	O
,	O
but	O
the	O
first	O
release	O
of	O
Exchange	O
(	O
Exchange	O
Server	O
4.0	O
in	O
April	O
1996	O
)	O
was	O
an	O
entirely	O
new	O
X.400-based	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
groupware	B-Application
system	O
with	O
a	O
single	O
database	O
store	O
,	O
which	O
also	O
supported	O
X.500	B-Protocol
directory	I-Protocol
services	O
.	O
</s>
<s>
The	O
directory	O
used	O
by	O
Exchange	O
Server	O
eventually	O
became	O
Microsoft	O
's	O
Active	B-Protocol
Directory	I-Protocol
service	I-Protocol
,	O
an	O
LDAP-compliant	O
directory	O
service	O
which	O
was	O
integrated	O
into	O
Windows	B-Application
2000	I-Application
as	O
the	O
foundation	O
of	O
Windows	B-General_Concept
Server	I-General_Concept
domains	I-General_Concept
.	O
</s>
<s>
The	O
current	O
version	O
,	O
Exchange	O
Server	B-Device
2019	I-Device
,	O
was	O
released	O
in	O
October	O
2018	O
.	O
</s>
<s>
Unlike	O
other	O
Office	O
Server	B-Device
2019	I-Device
products	O
such	O
as	O
SharePoint	O
and	O
Skype	B-Protocol
for	I-Protocol
Business	I-Protocol
,	O
Exchange	O
Server	B-Device
2019	I-Device
could	O
only	O
be	O
deployed	O
on	O
Windows	B-Device
Server	I-Device
2019	I-Device
when	O
it	O
was	O
released	O
.	O
</s>
<s>
Since	O
Cumulative	O
Update	O
2022	O
H1	O
Exchange	O
2019	O
has	O
been	O
supported	O
on	O
Windows	B-Device
Server	I-Device
2022	O
.	O
</s>
<s>
One	O
of	O
the	O
key	O
features	O
of	O
the	O
new	O
release	O
is	O
that	O
Exchange	O
Server	O
can	O
be	O
deployed	O
onto	O
Windows	B-Device
Server	I-Device
Core	O
for	O
the	O
first	O
time	O
.	O
</s>
<s>
Additionally	O
,	O
Microsoft	O
has	O
retired	O
the	O
Unified	O
Messaging	O
feature	O
of	O
Exchange	O
,	O
meaning	O
that	O
Skype	B-Protocol
for	I-Protocol
Business	I-Protocol
on-premises	B-General_Concept
customers	O
will	O
have	O
to	O
use	O
alternative	O
solutions	O
for	O
voicemail	O
,	O
such	O
as	O
Azure	O
cloud	O
voicemail	O
.	O
</s>
<s>
Exchange	O
Server	O
Enterprise	O
Edition	O
supports	O
clustering	O
of	O
up	O
to	O
4	O
nodes	O
when	O
using	O
Windows	B-Application
2000	I-Application
Server	O
,	O
and	O
up	O
to	O
8	O
nodes	O
with	O
Windows	B-Device
Server	I-Device
2003	O
.	O
</s>
<s>
In	O
this	O
scenario	O
,	O
the	O
data	O
can	O
be	O
regarded	O
as	O
a	O
single	B-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
,	O
despite	O
Microsoft	O
's	O
description	O
of	O
this	O
set-up	O
as	O
a	O
"	O
Shared	O
Nothing	O
"	O
model	O
.	O
</s>
<s>
Exchange	O
Server	O
2007	O
provides	O
built-in	O
support	O
for	O
asynchronous	O
replication	O
modeled	O
on	O
SQL	O
Server	O
's	O
"	O
Log	B-General_Concept
shipping	I-General_Concept
"	O
in	O
CCR	O
(	O
Cluster	O
Continuous	O
Replication	O
)	O
clusters	O
,	O
which	O
are	O
built	O
on	O
MSCS	O
MNS	O
(	O
Microsoft	O
Cluster	O
Service	O
—	O
Majority	O
Node	O
Set	O
)	O
clusters	O
,	O
which	O
do	O
not	O
require	O
shared	O
storage	O
.	O
</s>
<s>
Like	O
Windows	B-Device
Server	I-Device
products	O
,	O
Exchange	O
Server	O
requires	O
client	B-License
access	I-License
licenses	I-License
,	O
which	O
are	O
different	O
from	O
Windows	O
CALs	O
.	O
</s>
<s>
Just	O
like	O
Windows	B-Device
Server	I-Device
and	O
other	O
server	O
products	O
from	O
Microsoft	O
,	O
there	O
is	O
the	O
choice	O
to	O
use	O
User	O
CALs	O
or	O
Device	O
CALs	O
.	O
</s>
<s>
Microsoft	O
Exchange	O
Server	O
uses	O
a	O
proprietary	B-Application
remote	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
(	O
RPC	O
)	O
protocol	O
called	O
MAPI/RPC	B-Protocol
,	O
which	O
was	O
designed	O
to	O
be	O
used	O
by	O
Microsoft	B-Application
Outlook	I-Application
.	O
</s>
<s>
Clients	O
capable	O
of	O
using	O
the	O
proprietary	B-Application
features	O
of	O
Exchange	O
Server	O
include	O
Evolution	B-Language
,	O
Hiri	B-Language
and	O
Microsoft	B-Application
Outlook	I-Application
.	O
</s>
<s>
Thunderbird	B-Application
can	O
access	O
Exchange	O
server	O
via	O
the	O
Owl	O
Plugin	O
.	O
</s>
<s>
Exchange	O
Web	O
Services	O
(	O
EWS	O
)	O
,	O
an	O
alternative	O
to	O
the	O
MAPI	B-Protocol
protocol	O
,	O
is	O
a	O
documented	O
SOAP-based	O
protocol	O
introduced	O
with	O
Exchange	O
Server	O
2007	O
.	O
</s>
<s>
Exchange	O
Web	O
Services	O
is	O
used	O
by	O
the	O
latest	O
version	O
of	O
Microsoft	B-Application
Entourage	I-Application
for	O
Mac	O
and	O
Microsoft	B-Application
Outlook	I-Application
for	O
Mac	O
-	O
since	O
the	O
release	O
of	O
Mac	B-Device
OS	I-Device
X	I-Device
Snow	I-Device
Leopard	I-Device
Mac	O
computers	O
running	O
OS	O
X	O
include	O
some	O
support	O
for	O
this	O
technology	O
via	O
Apple	O
's	O
Mail	B-Operating_System
application	O
.	O
</s>
<s>
E-mail	O
hosted	O
on	O
an	O
Exchange	O
Server	O
can	O
also	O
be	O
accessed	O
using	O
POP3	B-Protocol
,	O
and	O
IMAP4	B-Protocol
protocols	O
,	O
using	O
clients	O
such	O
as	O
Windows	B-Application
Live	I-Application
Mail	I-Application
,	O
Mozilla	B-Application
Thunderbird	I-Application
,	O
and	O
Lotus	B-Operating_System
Notes	I-Operating_System
.	O
</s>
<s>
Exchange	O
Server	O
mailboxes	O
can	O
also	O
be	O
accessed	O
through	O
a	O
web	O
browser	O
,	O
using	O
Outlook	B-Protocol
Web	I-Protocol
App	I-Protocol
(	O
OWA	O
)	O
.	O
</s>
<s>
Exchange	O
Server	O
2003	O
also	O
featured	O
a	O
version	O
of	O
OWA	O
for	O
mobile	B-Application
devices	I-Application
,	O
called	O
Outlook	B-Application
Mobile	I-Application
Access	O
(	O
OMA	O
)	O
.	O
</s>
<s>
Microsoft	O
Exchange	O
Server	O
up	O
to	O
version	O
5.0	O
came	O
bundled	O
with	O
Microsoft	B-Application
Exchange	I-Application
Client	I-Application
as	O
the	O
email	B-Protocol
client	I-Protocol
.	O
</s>
<s>
After	O
version	O
5.0	O
,	O
this	O
was	O
replaced	O
by	O
Microsoft	B-Application
Outlook	I-Application
,	O
bundled	O
as	O
part	O
of	O
Microsoft	B-Operating_System
Office	I-Operating_System
97	I-Operating_System
and	O
later	O
.	O
</s>
<s>
The	O
original	O
Windows	B-Application
95	I-Application
"	O
Inbox	O
"	O
client	O
also	O
used	O
MAPI	B-Protocol
and	O
was	O
called	O
"	O
Microsoft	O
Exchange	O
"	O
.	O
</s>
<s>
A	O
stripped-down	O
version	O
of	O
the	O
Exchange	O
Client	O
that	O
does	O
not	O
have	O
support	O
for	O
Exchange	O
Server	O
was	O
released	O
as	O
Windows	B-Application
Messaging	I-Application
to	O
avoid	O
confusion	O
;	O
it	O
was	O
included	O
with	O
Windows	B-Application
95	I-Application
OSR2	O
,	O
Windows	B-Device
98	I-Device
,	O
and	O
Windows	B-Device
NT	I-Device
4	I-Device
.	O
</s>
<s>
It	O
was	O
discontinued	O
because	O
of	O
the	O
move	O
to	O
email	O
standards	O
such	O
as	O
SMTP	B-Protocol
,	O
IMAP	B-Protocol
,	O
and	O
POP3	B-Protocol
,	O
all	O
of	O
which	O
Outlook	B-Application
Express	I-Application
supports	O
better	O
than	O
Windows	B-Application
Messaging	I-Application
.	O
</s>
<s>
Support	O
for	O
Exchange	B-Protocol
ActiveSync	I-Protocol
(	O
EAS	B-Protocol
)	O
was	O
added	O
to	O
Microsoft	O
Exchange	O
Server	O
2003	O
.	O
</s>
<s>
It	O
allows	O
a	O
compliant	O
device	O
such	O
as	O
a	O
Windows	B-Operating_System
Mobile	I-Operating_System
device	O
or	O
smartphone	B-Application
to	O
securely	O
synchronize	O
mail	B-Operating_System
,	O
contacts	O
and	O
other	O
data	O
directly	O
with	O
an	O
Exchange	O
server	O
and	O
has	O
become	O
a	O
popular	O
mobile	O
access	O
standard	O
for	O
businesses	O
due	O
to	O
support	O
from	O
companies	O
like	O
Nokia	O
and	O
Apple	O
Inc	O
.	O
as	O
well	O
as	O
its	O
device	O
security	O
and	O
compliance	O
features	O
.	O
</s>
<s>
Support	O
for	O
push	B-General_Concept
email	I-General_Concept
was	O
added	O
to	O
it	O
with	O
Exchange	O
Server	O
2003	O
Service	O
Pack	O
2	O
and	O
is	O
supported	O
by	O
Windows	O
Phone	O
7	O
,	O
the	O
iPhone	B-Device
and	O
Android	B-Application
phones	I-Application
,	O
but	O
notably	O
not	O
for	O
Apple	O
's	O
native	O
Mail	B-Operating_System
app	O
on	O
macOS	B-Application
.	O
</s>
<s>
Exchange	B-Protocol
ActiveSync	I-Protocol
Policies	O
allow	O
administrators	O
to	O
control	O
which	O
devices	O
can	O
connect	O
to	O
the	O
organization	O
,	O
remotely	O
deactivate	O
features	O
,	O
and	O
remotely	O
wipe	O
lost	O
or	O
stolen	O
devices	O
.	O
</s>
<s>
The	O
complexities	O
of	O
managing	O
Exchange	O
Server	O
--	O
namely	O
running	O
both	O
one	O
or	O
more	O
Exchange	O
Servers	O
,	O
plus	O
Active	B-Protocol
Directory	I-Protocol
synchronization	O
servers	O
--	O
make	O
it	O
attractive	O
for	O
organisations	O
to	O
purchase	O
it	O
as	O
a	O
hosted	O
service	O
.	O
</s>
<s>
This	O
has	O
been	O
possible	O
from	O
a	O
number	O
of	O
providers	O
for	O
more	O
than	O
10	O
years	O
,	O
but	O
as	O
of	O
June	O
2018	O
is	O
that	O
many	O
providers	O
have	O
been	O
marketing	O
the	O
service	O
as	O
"	O
cloud	O
computing	O
"	O
or	O
"	O
Software-as-a-Service	B-Architecture
"	O
.	O
</s>
<s>
It	O
is	O
built	O
on	O
the	O
same	O
technologies	O
as	O
on-premises	B-General_Concept
Exchange	O
Server	O
,	O
and	O
offers	O
essentially	O
the	O
same	O
services	O
as	O
third-party	O
providers	O
which	O
host	O
Exchange	O
Server	O
instances	O
.	O
</s>
<s>
Customers	O
can	O
also	O
choose	O
to	O
combine	O
both	O
on-premises	B-General_Concept
and	O
online	O
options	O
in	O
a	O
hybrid	O
deployment	O
.	O
</s>
<s>
Hybrid	O
implementations	O
are	O
popular	O
for	O
organizations	O
that	O
are	O
unsure	O
of	O
the	O
need	O
or	O
urgency	O
to	O
do	O
a	O
full	O
transition	O
to	O
Exchange	O
Online	O
,	O
and	O
also	O
allows	O
for	O
staggered	O
email	B-Protocol
migration	I-Protocol
.	O
</s>
<s>
Hybrid	O
tools	O
can	O
cover	O
the	O
main	O
stack	O
of	O
Microsoft	O
Exchange	O
,	O
Lync	B-Protocol
,	O
SharePoint	O
,	O
Windows	O
,	O
and	O
Active	B-Protocol
Directory	I-Protocol
servers	O
,	O
in	O
addition	O
to	O
using	O
replica	O
data	O
to	O
report	O
cloud	O
user	O
experience	O
.	O
</s>
<s>
In	O
June	O
2011	O
,	O
as	O
part	O
of	O
the	O
commercial	O
release	O
of	O
Microsoft	B-Operating_System
Office	I-Operating_System
365	I-Operating_System
,	O
Exchange	O
Online	O
was	O
updated	O
with	O
the	O
capabilities	O
of	O
Exchange	O
Server	O
2010	O
.	O
</s>
<s>
In	O
February	O
2020	O
,	O
an	O
ASP.NET	B-Application
vulnerability	O
was	O
discovered	O
and	O
exploited	O
relying	O
on	O
a	O
default	O
setting	O
allowing	O
attackers	O
to	O
run	O
arbitrary	O
code	O
with	O
system	O
privileges	O
,	O
only	O
requiring	O
a	O
connection	O
to	O
the	O
server	O
as	O
well	O
as	O
being	O
logged	O
into	O
any	O
user	O
account	O
which	O
can	O
be	O
done	O
through	O
credential	O
stuffing	O
.	O
</s>
<s>
The	O
exploit	O
relied	O
on	O
all	O
versions	O
of	O
Microsoft	O
Exchange	O
using	O
the	O
same	O
static	B-General_Concept
validation	O
key	O
to	O
decrypt	O
,	O
encrypt	O
,	O
and	O
validate	O
the	O
'	O
View	O
State	O
 '	O
by	O
default	O
on	O
all	O
installations	O
of	O
the	O
software	O
and	O
all	O
versions	O
of	O
it	O
,	O
where	O
the	O
View	O
State	O
is	O
used	O
to	O
temporarily	O
preserve	O
changes	O
to	O
an	O
individual	O
page	O
as	O
information	O
is	O
sent	O
to	O
the	O
server	O
.	O
</s>
<s>
When	O
logged	O
in	O
as	O
any	O
user	O
,	O
any	O
.ASPX	B-Application
page	O
is	O
then	O
loaded	O
,	O
and	O
by	O
requesting	O
both	O
the	O
session	B-Protocol
ID	I-Protocol
of	O
the	O
user	O
login	O
and	O
the	O
correct	O
View	O
State	O
directly	O
from	O
the	O
server	O
,	O
this	O
correct	O
View	O
State	O
can	O
be	O
deserialised	B-Application
and	O
then	O
modified	O
to	O
also	O
include	O
arbitrary	O
code	O
and	O
then	O
be	O
falsely	O
verified	O
by	O
the	O
attacker	O
.	O
</s>
<s>
This	O
modified	O
View	O
State	O
is	O
then	O
serialised	O
and	O
passed	O
back	O
to	O
the	O
server	O
in	O
a	O
GET	O
request	O
along	O
with	O
the	O
session	B-Protocol
ID	I-Protocol
to	O
show	O
it	O
is	O
from	O
a	O
logged-in	O
user	O
;	O
in	O
legitimate	O
use	O
,	O
the	O
view	O
state	O
should	O
always	O
be	O
returned	O
in	O
a	O
POST	B-Protocol
request	I-Protocol
,	O
and	O
never	O
a	O
GET	O
request	O
.	O
</s>
