<s>
The	O
comparison	B-Application
of	I-Application
mail	I-Application
servers	I-Application
covers	O
mail	B-Protocol
transfer	I-Protocol
agents	I-Protocol
(	O
MTAs	O
)	O
,	O
mail	B-Protocol
delivery	I-Protocol
agents	I-Protocol
,	O
and	O
other	O
computer	B-Application
software	I-Application
that	O
provide	O
e-mail	B-Protocol
services	I-Protocol
.	O
</s>
<s>
Unix-based	O
mail	B-Protocol
servers	I-Protocol
are	O
built	O
using	O
a	O
number	O
of	O
components	O
because	O
a	O
Unix-style	O
environment	O
is	O
,	O
by	O
default	O
,	O
a	O
toolbox	B-Operating_System
operating	O
system	O
.	O
</s>
<s>
A	O
stock	O
Unix-like	O
server	O
already	O
has	O
internal	O
mail	O
;	O
more	O
traditional	O
ones	O
also	O
come	O
with	O
a	O
full	O
MTA	B-Protocol
already	O
part	O
of	O
the	O
standard	O
installation	O
.	O
</s>
<s>
To	O
allow	O
the	O
server	O
to	O
send	O
external	O
emails	O
,	O
an	O
MTA	B-Protocol
such	O
as	O
Sendmail	B-Application
,	O
Postfix	B-Application
,	O
or	O
Exim	B-Protocol
is	O
required	O
.	O
</s>
<s>
Mail	O
is	O
read	O
either	O
through	O
direct	O
access	O
(	O
shell	B-Operating_System
login	O
)	O
or	O
mailbox	O
protocols	O
like	O
POP	B-Protocol
and	O
IMAP	B-Protocol
.	O
</s>
<s>
Unix-based	O
MTA	B-Protocol
software	O
largely	O
acts	O
to	O
enhance	O
or	O
replace	O
the	O
respective	O
system	O
's	O
native	O
MTA	B-Protocol
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
servers	O
do	O
not	O
natively	O
implement	O
e-mail	O
,	O
thus	O
Windows-based	O
MTAs	O
have	O
to	O
supply	O
all	O
the	O
necessary	O
aspects	O
of	O
e-mail-related	O
functionality	O
.	O
</s>
<s>
License	B-License
Mail	B-Protocol
server	I-Protocol
Linux/Unix	O
Windows	B-Application
macOS	B-Application
SMTP	B-Protocol
POP3	B-Protocol
IMAP	B-Protocol
JMAP	B-Protocol
IDLE	B-Protocol
SMTPS	B-Protocol
POP3S	B-Protocol
IPv6	B-Protocol
SSL	B-Protocol
DANE	B-Protocol
Webmail	B-Protocol
ActiveSync	B-Protocol
Sieve	O
IDN/UTF8	O
Database	O
File-based	B-Application
agorum	B-Protocol
core	I-Protocol
Apache	B-Language
James	I-Language
Axigen	B-Application
(	O
free	O
version	O
:	O
5	O
domains	O
,	O
5	O
users	O
,	O
5	O
groups	O
)	O
Citadel	B-Protocol
CommuniGate	B-Protocol
Pro	I-Protocol
(	O
Free	O
for	O
up	O
to	O
5	O
users	O
)	O
Courier	B-Protocol
Mail	I-Protocol
Server	I-Protocol
Cyrus	B-Protocol
IMAP	I-Protocol
Dovecot	B-Language
Dovecot	B-Language
Operating	O
System	O
Compatibility	O
.	O
</s>
<s>
Dovecot	B-Language
Submission	O
Service	O
.	O
</s>
<s>
Eudora	B-Application
Internet	I-Application
Mail	I-Application
Server	I-Application
Exim	B-Protocol
(	O
via	O
Cygwin	O
)	O
See	O
NOTICE	O
file	O
in	O
the	O
distribution	O
FirstClass	B-Protocol
Gordano	B-Protocol
Messaging	I-Protocol
Suite	I-Protocol
GroupWise	B-Operating_System
Halon	B-Application
Haraka	B-Protocol
hMailServer	B-Language
IBM	B-Operating_System
Lotus	I-Operating_System
Domino	I-Operating_System
IceWarp	B-Protocol
Mail	I-Protocol
Server	I-Protocol
Ipswitch	B-Application
IMail	I-Application
Server	I-Application
(	O
since	O
v12.2	O
)	O
Kerio	B-Protocol
Connect	I-Protocol
Kolab	B-Language
Kopano	B-Protocol
Mailsite	B-Protocol
Mailtraq	B-Device
MDaemon	B-Protocol
Mercury	B-Application
Mail	I-Application
Transport	I-Application
System	I-Application
Microsoft	B-Operating_System
Exchange	I-Operating_System
Server	I-Operating_System
3rd	O
Party	O
support	O
NetMail	B-Protocol
OpenSMTPD	B-Application
Open-Xchange	B-Protocol
Oracle	B-Application
Communications	I-Application
Messaging	I-Application
Server	I-Application
Postfix	B-Application
qmail	B-Application
via	O
Qsmtp	O
Qpopper	B-Protocol
(	O
via	O
Cygwin	O
)	O
Contains	O
jurisdiction	O
selection	O
and	O
IPL-style	O
indemnification	O
clause	O
.	O
</s>
<s>
Scalix	B-Protocol
(	O
via	O
Stunnel	B-Protocol
)	O
(	O
via	O
Stunnel	B-Protocol
)	O
(	O
via	O
Stunnel	B-Protocol
)	O
Sendmail	B-Application
(	O
since	O
8.16	O
)	O
Sendmail	B-Application
Release	O
Notes	O
.	O
</s>
<s>
Mail	B-Protocol
server	I-Protocol
SMTP	B-Protocol
AUTH	O
POP	B-Protocol
before	O
SMTP	B-Protocol
APOP	B-Protocol
File	B-Application
System	I-Application
Database	O
LDAP	B-Protocol
Native	O
Anti	O
Hammer	O
-	O
Brute-force	O
attack	O
protection	O
Other	O
agorum	B-Protocol
core	I-Protocol
PLAIN	O
,	O
LOGIN	O
,	O
CRAM-MD5	O
,	O
CRAM-MD5	O
to	O
Historic	O
,	O
20	O
November	O
2008	O
.	O
</s>
<s>
NTLM	O
Apache	B-Language
James	I-Language
PLAIN	O
,	O
LOGIN	O
Axigen	B-Application
GSSAPI	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
Moving	O
DIGEST-MD5	B-Protocol
to	O
Historic	O
,	O
July	O
2011	O
.	O
</s>
<s>
APOP	B-Protocol
,	O
CLRTXT	O
,	O
LOGIN	O
,	O
PLAIN	O
,	O
LDAP	B-Protocol
,	O
Internal	O
CommuniGate	B-Protocol
Pro	I-Protocol
Active	B-Protocol
Directory	I-Protocol
(	O
LDAP	B-Protocol
)	O
,	O
CLRTXT	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
APOP	B-Protocol
,	O
GSSAPI	O
,	O
NTLM	O
,	O
MSN	O
,	O
SESSIONID	O
,	O
External	O
Authentication	O
Plug-in	O
.	O
</s>
<s>
Also	O
supports	O
X.509	O
PKI	O
auth	O
via	O
STARTTLS/SSL	O
Courier	B-Protocol
Mail	I-Protocol
Server	I-Protocol
Managed	O
by	O
Courier	O
authentication	O
library	O
which	O
can	O
use	O
PAM	B-Application
,	O
Userdb	O
,	O
PostgreSQL(beta )	O
,	O
MySQL	B-Application
,	O
LDAP	B-Protocol
,	O
and	O
EXTERNAL	O
.	O
</s>
<s>
Cyrus	B-Protocol
IMAP	I-Protocol
Supports	O
X.509	O
PKI	O
auth	O
via	O
STARTTLS	B-Protocol
and	O
EXTERNAL	O
.	O
</s>
<s>
Uses	O
Cyrus	B-Protocol
SASL	O
authentication	O
library	O
for	O
support	O
for	O
other	O
mechanisms	O
:	O
Berkeley	B-Language
DB	I-Language
,	O
GDBM	O
,	O
or	O
NDBM	O
(	O
sasldb	O
)	O
,	O
PAM	B-Application
,	O
MySQL	B-Application
,	O
PostgreSQL	B-Application
,	O
SQLite	B-Language
,	O
LDAP	B-Protocol
,	O
Active	O
Directory(LDAP )	O
,	O
DCE	B-Operating_System
,	O
Kerberos	B-Protocol
4	O
and	O
5	O
,	O
proxied	O
IMAP	B-Protocol
auth	O
,	O
getpwent	O
,	O
shadow	O
,	O
SIA	O
,	O
Courier	O
Authdaemon	O
,	O
httpform	O
,	O
APOP	B-Protocol
and	O
SASL	O
mechanisms	O
:	O
ANONYMOUS	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
SCRAM-SHA-1(-PLUS )	O
,	O
SCRAM-SHA-224(-PLUS )	O
,	O
SCRAM-SHA-256(-PLUS )	O
,	O
SCRAM-SHA-384(-PLUS )	O
,	O
SCRAM-SHA-512(-PLUS )	O
,	O
EXTERNAL	O
,	O
GSSAPI	O
,	O
LOGIN	O
,	O
NTLM	O
,	O
OTP	O
,	O
PASSDSS	O
,	O
PLAIN	O
,	O
SRP	O
Dovecot	B-Language
Submission	O
service	O
supports	O
SMTP	B-Protocol
AUTH	O
.	O
</s>
<s>
POP-before-SMTP	O
via	O
DRAC	O
plugin	O
.	O
</s>
<s>
PAM	B-Application
,	O
MySQL	B-Application
,	O
PostgreSQL	B-Application
,	O
SQLite	B-Language
,	O
LDAP	B-Protocol
,	O
Active	O
Directory(LDAP )	O
,	O
Kerberos	B-Protocol
5	I-Protocol
,	O
proxied	O
IMAP	B-Protocol
auth	O
,	O
getpwent	O
,	O
shadow	O
,	O
SIA	O
,	O
BSDauth	O
,	O
Vpopmail	B-Protocol
.	O
</s>
<s>
APOP	B-Protocol
and	O
SASL	O
mechanisms	O
:	O
ANONYMOUS	O
,	O
PLAIN	O
,	O
LOGIN	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
SCRAM-SHA-1	B-Protocol
,	O
EXTERNAL	O
,	O
GSSAPI	O
,	O
NTLM	O
,	O
OTP	O
,	O
SKEY	O
,	O
RPA	O
.	O
</s>
<s>
Eudora	B-Application
Internet	I-Application
Mail	I-Application
Server	I-Application
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
PLAIN	O
,	O
LOGIN	O
Exim	B-Protocol
Cyrus	B-Protocol
SASL	O
,	O
Dovecot	B-Language
SASL	O
,	O
GNU	O
SASL	O
,	O
CRAM-MD5	O
,	O
Heimdal	O
GSSAPI	O
,	O
PLAIN	O
,	O
LOGIN	O
,	O
SPA	O
FirstClass	B-Protocol
Gordano	B-Protocol
Messaging	I-Protocol
Suite	I-Protocol
PLAIN	O
,	O
LOGIN	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
APOP	B-Protocol
,	O
ODBC	O
,	O
Active	B-Protocol
Directory	I-Protocol
,	O
NT	O
Domain	O
GroupWise	B-Operating_System
eDirectory	B-Application
,	O
Any	O
LDAPv3-compliant	O
source	O
Halon	B-Application
Many	O
mechanism	O
(	O
SMTP	B-Protocol
callout	O
,	O
Dovecot	B-Language
SASL	O
,	O
REST	O
,	O
etc	O
.	O
)	O
</s>
<s>
Haraka	B-Protocol
Proxy	O
to	O
other	O
server	O
,	O
any	O
other	O
mechanism	O
via	O
AUTH	O
plugins	O
.	O
</s>
<s>
IceWarp	B-Protocol
Mail	I-Protocol
Server	I-Protocol
PLAIN	O
,	O
LOGIN	O
,	O
CRAM-MD5	O
,	O
NTLM	O
Ipswitch	B-Application
IMail	I-Application
Server	I-Application
Active	B-Protocol
Directory	I-Protocol
,	O
Windows	B-Application
authentication	O
,	O
CRAM-MD5	O
,	O
PLAIN	O
,	O
LOGIN	O
Kolab	B-Language
Kolab	B-Language
employs	O
Cyrus	B-Protocol
and	O
Postfix	B-Application
and	O
thus	O
supports	O
all	O
Cyrus	B-Protocol
SASL	O
authentication	O
methods	O
and	O
X.509	O
PKI	O
auth	O
via	O
STARTTLS	B-Protocol
and	O
EXTERNAL	O
.	O
</s>
<s>
Mailsite	B-Protocol
NT	O
Domain	O
,	O
Active	B-Protocol
Directory	I-Protocol
,	O
PLAIN	O
,	O
LOGIN	O
,	O
NTLM	O
,	O
SCRAM-MD5	B-Protocol
,	O
CRAM-MD5	O
Mailtraq	B-Device
NT	O
Domain	O
,	O
Active	B-Protocol
Directory	I-Protocol
,	O
Local	O
Directory	O
MDaemon	B-Protocol
Mercury	B-Application
Mail	I-Application
Transport	I-Application
System	I-Application
Internal	O
,	O
LOGIN	O
,	O
PLAIN	O
,	O
CRAM-MD5	O
,	O
Netware	O
,	O
LDAP	B-Protocol
?,	O
partial	O
NT	O
Domain	O
Microsoft	B-Operating_System
Exchange	I-Operating_System
Server	I-Operating_System
Active	B-Protocol
Directory	I-Protocol
,	O
LOGIN	O
,	O
NTLM	O
NetMail	B-Protocol
eDirectory	B-Application
,	O
LDAP	B-Protocol
Oracle	B-Application
Communications	I-Application
Messaging	I-Application
Server	I-Application
Plain	O
,	O
Login	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
Certificate	O
OpenSMTPD	B-Application
By	O
default	O
PLAIN	O
and	O
LOGIN	O
over	O
SSL	B-Protocol
only	O
,	O
Certificates	O
,	O
bsd_auth	O
and	O
PAM	B-Application
.	O
</s>
<s>
Postfix	B-Application
Supports	O
all	O
Cyrus	B-Protocol
SASL	O
authentication	O
methods	O
except	O
for	O
APOP	B-Protocol
.	O
</s>
<s>
Qpopper	B-Protocol
Pluggable	B-Application
Authentication	I-Application
Modules	I-Application
,	O
GSSAPI	O
,	O
CRAM-MD5	O
,	O
DIGEST-MD5	B-Protocol
,	O
APOP	B-Protocol
,	O
PLAIN	O
,	O
LDAP	B-Protocol
,	O
CMU	O
SASL	O
library	O
,	O
Kerberos	B-Protocol
qmail	B-Application
Works	O
with	O
any	O
checkpassword	O
utility	O
.	O
</s>
<s>
Alternate	O
checkpassword	O
utilities	O
support	O
authentication	O
against	O
PAM	B-Application
,	O
LDAP	B-Protocol
,	O
and	O
databases	O
.	O
</s>
<s>
Scalix	B-Protocol
Internal	O
,	O
LOGIN	O
,	O
PLAIN	O
,	O
X.500	B-Protocol
(	O
DAP	B-Protocol
)	O
,	O
LDAP	B-Protocol
,	O
OpenLDAP	B-Language
,	O
Active	B-Protocol
Directory	I-Protocol
,	O
eDirectory	B-Application
,	O
Kerberos	B-Protocol
,	O
etc	O
.	O
</s>
<s>
Sendmail	B-Application
Supports	O
all	O
Cyrus	B-Protocol
SASL	O
authentication	O
methods	O
except	O
for	O
APOP	B-Protocol
.	O
</s>
<s>
Also	O
supports	O
X.509	O
PKI	O
auth	O
via	O
STARTTLS	B-Protocol
and	O
EXTERNAL	O
.	O
</s>
<s>
Mail	B-Protocol
Server	I-Protocol
DNSBL	O
SURBL	O
Spamtraps	O
Greylisting	O
SPF	B-Protocol
DKIM	B-Protocol
DMARC	O
Tarpit	O
Bayesian	B-Application
filters	I-Application
Regular	B-Language
expressions	I-Language
Embedded	B-Application
Antivirus	I-Application
Embedded	O
Antispam	O
agorum	B-Protocol
core	I-Protocol
Apache	B-Language
James	I-Language
ClamAV	B-Application
(	O
Apache	B-Language
SpamAssassin	I-Language
)	O
Axigen	B-Application
,	O
in	O
SpamAssassin	B-Language
CYREN	O
CYREN	O
Citadel	B-Protocol
(	O
via	O
SpamAssassin	B-Language
)	O
(	O
via	O
SpamAssassin	B-Language
)	O
(	O
ClamAV	B-Application
)	O
(	O
SpamAssassin	B-Language
)	O
Courier	B-Protocol
Mail	I-Protocol
Server	I-Protocol
Two	O
DKIM	B-Protocol
filters	O
can	O
be	O
found	O
in	O
Courier-MTA	B-Protocol
'	O
s	O
links	O
page	O
With	O
Clamav	B-Application
Dovecot	B-Language
Considered	O
and	O
rejected	O
by	O
developers	O
in	O
2013	O
.	O
</s>
<s>
Eudora	B-Application
Internet	I-Application
Mail	I-Application
Server	I-Application
Exim	B-Protocol
(	O
at	O
build	O
time	O
,	O
most	O
distributions	O
do	O
)	O
(	O
at	O
build	O
time	O
,	O
most	O
distributions	O
do	O
)	O
(	O
at	O
build	O
time	O
,	O
most	O
distributions	O
do	O
)	O
with	O
spamassassin	B-Language
etc	O
.	O
</s>
<s>
any	O
any	O
FirstClass	B-Protocol
Symantec	O
Gordano	B-Protocol
Messaging	I-Protocol
Suite	I-Protocol
CYREN	O
,	O
Authentium	O
CYREN	O
GroupWise	B-Operating_System
Halon	B-Application
(	O
via	O
SpamAssassin	B-Language
)	O
(	O
Sophos	O
,	O
ClamAV	B-Application
)	O
(	O
CYREN	O
,	O
SpamAssassin	B-Language
)	O
Haraka	B-Protocol
with	O
spamassassin	B-Language
etc	O
.	O
</s>
<s>
ClamAV	B-Application
,	O
AVG	B-Application
,	O
any	O
via	O
plugins	O
SpamAssassin	B-Language
,	O
MessageSniffer	O
hMailServer	B-Language
ClamAV	B-Application
SpamAssassin	B-Language
IBM	B-Operating_System
Notes	I-Operating_System
IceWarp	B-Protocol
Mail	I-Protocol
Server	I-Protocol
Ipswitch	B-Application
IMail	I-Application
Server	I-Application
Symantec	O
,	O
BitDefender	B-Application
CYREN	O
Kolab	B-Language
with	O
spamassassin	B-Language
etc	O
.	O
</s>
<s>
(	O
via	O
content	O
filter	O
interface	O
)	O
(	O
via	O
content	O
filter	O
interface	O
)	O
Mailsite	B-Protocol
Mailtraq	B-Device
MDaemon	B-Protocol
(	O
via	O
SpamAssassin	B-Language
)	O
(	O
via	O
SpamAssassin	B-Language
)	O
(	O
via	O
Content	O
Filter	O
)	O
Cyren	O
,	O
ClamAV	B-Application
SpamAssassin	B-Language
Mercury	B-Application
Mail	I-Application
Transport	I-Application
System	I-Application
(	O
GreyWall	O
extension	O
)	O
(	O
SpamHalter	O
extension	O
)	O
(	O
ClamWall	O
extension	O
)	O
Microsoft	B-Operating_System
Exchange	I-Operating_System
Server	I-Operating_System
(	O
2003	O
&	O
later	O
)	O
(	O
Signing	O
only	O
via	O
3rd	O
Party	O
Extensions	O
)	O
(	O
2003	O
&	O
later	O
)	O
NetMail	B-Protocol
OpenSMTPD	B-Application
With	O
or	O
With	O
Oracle	B-Application
Communications	I-Application
Messaging	I-Application
Server	I-Application
with	O
spamassassin	B-Language
etc	O
.	O
</s>
<s>
any	O
any	O
Postfix	B-Application
with	O
spamassassin	B-Language
etc	O
.	O
</s>
<s>
(	O
via	O
content	O
filter	O
interface	O
)	O
(	O
via	O
content	O
filter	O
interface	O
)	O
qmail	B-Application
Scalix	B-Protocol
(	O
via	O
Scalix	B-Protocol
AntiSpam	O
powered	O
by	O
Cyren	O
or	O
SpamAssassin	B-Language
)	O
(	O
via	O
Scalix	B-Protocol
AntiSpam	O
powered	O
by	O
Cyren	O
or	O
SpamAssassin	B-Language
)	O
(	O
via	O
Scalix	B-Protocol
ZeroHour	O
AntiVirus	B-Application
powered	O
by	O
Cyren	O
or	O
ClamAV	B-Application
)	O
Sendmail	B-Application
(	O
via	O
milter/SA	O
)	O
with	O
spamassassin	B-Language
etc	O
.	O
</s>
