Comparison of mail servers

The comparison of mail servers covers mail transfer agents, mail delivery agents, and other computer software that provide e-mail services.

Unix-based mail servers are built using a number of components because a Unix-style environment is, by default, a toolbox[1] operating system. A stock Unix-like server already has internal mail; more traditional ones also come with a full MTA already part of the standard installation. To allow the server to send external emails, an MTA such as Sendmail, Postfix, or Exim is required. Mail is read either through direct access (shell login) or mailbox protocols like POP and IMAP. Unix based MTA software largely acts as enhancement or replacement of the respective system's "native" MTA.

Microsoft Windows servers do not natively implement email. Windows-based MTAs therefore have to cover the whole set of email-related functionality.

Feature comparison

	Server OS support			Features												Storage		Users
Mail server	Linux/ Unix	Windows	Mac OS	SMTP	POP3	IMAP	JMAP	IMAP IDLE	SMTP over TLS	POP over TLS	IPv6	SSL	DANE	Webmail	ActiveSync	Sieve	Database	Filesystem	Other	IDN/UTF8	License
agorum core	Yes	Yes	No	Yes	No	Yes	?	No	No	No	No	Yes	No	Yes	No	No	Yes	No	No	?	GPLv2
Apache James	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	?	Yes	?	No	No	Yes	Yes	Yes	No	?	ASLv2
Axigen	Yes	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	?	Ajax, Basic & Mobile	Yes	Yes	Proprietary, Embedded, Optimized for Email & Groupware	Yes	Yes	Yes	Proprietary (free version: 5 domains, 5 users, 5 groups)
Citadel	Yes	No	Yes	Yes	Yes	Yes	?	No	Yes	Yes	Yes	Yes	?	Yes	No	Yes	Yes	No	No	?	GPLv3
CommuniGate Pro	Yes	Yes	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	?	Yes	Yes	?	Yes	Yes	Yes	Yes	Proprietary (Free for up to 5 users)
Courier Mail Server	Yes	No	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	No	Yes	No	maildrop	No	maildir	No	Yes	GPLv3[2]
Cyrus IMAP	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes[3]	Yes	Yes	Yes	?	No	No	Yes	Yes (indexes)	Yes	Yes	?	4-clause BSD[4]
Dovecot	Yes[5]	No	Yes	Yes[6]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	No	No	No	Yes	Yes	maildir, mbox, dbox, mdbox, obox[7]	S3, sproxyd, CDMI[7]	No	Mixed: MIT and LGPL 2.1[8]
Eudora Internet Mail Server	No	No	Yes	Yes	Yes	Yes	?	?	No	No	?	No	?	No	No	?	No	No	Yes	?	Proprietary
Exim	Yes	Yes (via Cygwin)	Yes	Yes	Dovecot, UW IMAP	Dovecot, UW IMAP	?	Dovecot, UW IMAP	Yes	No	Yes	Yes	Yes[9]	No	No	Yes	Yes	Yes	No	Yes	GPLv2+[10]
FirstClass	Yes	Yes	Yes	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	Yes	?	Yes	Yes	Yes	?	Proprietary
Gordano Messaging Suite	Yes	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	?	Yes	?	Yes	Yes	No	Yes	Yes	Yes	?	Proprietary
GroupWise	Yes	Yes	No	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	Yes	?	Yes	No	No	?	Proprietary
Halon	Yes	No	No	Yes	No	No	?	No	Yes	No	Yes	Yes	Yes[11]	No	No	?	Yes	Yes	Yes	Yes	Proprietary
Haraka	Yes	Yes	Yes	Yes	No	No	?	No	Yes	No	Yes	Yes	?	No	No	?	Yes	Yes	Yes	Yes	MIT
hMailServer	No	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	?	Yes	No	?	Yes	Yes	No	No	GNU AGPL
IBM Lotus Domino	Yes	Yes	No	Yes	Yes	Yes	?	No	Yes	Yes	Yes	Yes	No	Yes	No	?	Yes	No	No	No	Proprietary
IceWarp Mail Server	Yes	Yes	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	No	Yes	Yes	No	?	Proprietary
Ipswitch IMail Server	No	Yes	No	Yes	Yes	Yes	?	Yes (since v12.2)[12]	Yes	Yes	?	Yes	?	Yes	Yes	?	No	Yes	No	?	Proprietary
Kerio Connect	Yes	Yes	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	No	Yes	No	?	Proprietary
Kolab	Yes	No	No	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	?	GPLv3
Kopano	Yes	No	No	postfix, etc.[13]	Yes	Yes	No	Yes	postfix	Yes	Yes	Yes	postfix	Yes	z-push	No	SQL	Yes	Amazon S3	Yes	AGPLv3, paid[14]
Mailsite	No	Yes	No	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	Yes	Yes	Yes	Yes	Yes	?	Proprietary
Mailtraq	No	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	?	Yes	?	Yes	No	?	Yes	Yes	Yes	?	Proprietary
MDaemon	No	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	No	No	Yes	Yes	Not IMAP	Proprietary
Mercury Mail Transport System	No	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	No	Yes	No	Yes	No	No	No	Yes	No	No	Proprietary donationware
Microsoft Exchange Server	No	Yes	No	Yes	Yes	Yes	No	Yes[15][16]	Yes	Yes	Yes [17]	Yes	No	Yes	Yes	3rd Party support	Yes	Yes	Yes	Not IMAP	Proprietary
NetMail	Yes	Yes	No	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	No	?	Yes	No	No	?	Proprietary
OpenSMTPD	Yes	No	Yes	Yes	No	No	?	No	Yes	No	Yes	Yes	No[18]	No	No	?	possible through custom backends	Yes	No	No	ISC
Open-Xchange	Yes	No	No	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	Yes	?	Yes	No	No	?	Proprietary/SaaS, with open-source parts[19]
Oracle Communications Messaging Server	Yes	No	No	Yes	Yes	Yes	?	?	Yes	Yes	?	Yes	?	Yes	No	?	Yes	Yes	No	Yes	Proprietary
Postfix	Yes	No	Yes	Yes	Dovecot, UW IMAP	Dovecot, UW IMAP	?	Dovecot, UW IMAP	Yes	No	Yes	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	IBM Public License
qmail	Yes	No	Yes	Yes	Yes	Dovecot, UW IMAP	?	Dovecot, UW IMAP	No	Dovecot, UW IMAP	via Qsmtp	No	No	No	No	?	(cdb)	Yes	No	?	Public domain
Qpopper	Yes	Yes (via Cygwin)	Yes	No	Yes	No	?	No	No	Yes	?	Yes	?	No	No	?	No	Yes	Yes	?	BSD-style, GPL-incompatible[20]
Scalix	Yes	?	?	Yes	Yes	Yes	?	Yes	Yes (via Stunnel)	Yes (via Stunnel)	?	Yes (via Stunnel)	?	Yes	Yes	?	Yes	Yes	No	?	Proprietary with OSS parts, a community (Freeware) and 3 paid editions (SMB, Enterprise, Hosting)
Sendmail	Yes	No	Yes	Yes	Dovecot, UW IMAP	Dovecot, UW IMAP	?	Dovecot, UW IMAP	Yes	No	Yes	Yes	Yes (since 8.16)[21]	No	No	No	?	Yes	?	Yes	Sendmail License
SparkEngine	Yes	Yes	Yes	Yes	No	No	?	No	Yes	No	?	Yes	?	No	No	?	Yes	Yes	Yes	?	Proprietary
UW IMAP	Yes	Yes	Yes	No	Yes	Yes	?	Yes	No	Yes	Yes	Yes	No	WebPine	No	No	Yes (Indexes)	Yes	No	?	Apache License 2.0[22]
WinGate	No	Yes	No	Yes	Yes	Yes	?	Yes	Yes	Yes	No	Yes	?	Yes	No	?	No	Yes	No	?	Proprietary
Zarafa	Yes	No	No	postfix etc.[13]	Yes	Yes	No	Yes	postfix	Yes	Yes	Yes	postfix	Yes	z-push	No	SQL	Yes	Amazon S3	No	AGPLv3, paid[14]
Zentyal	Yes	No	No	Yes	Yes	Yes	?	Yes	Yes	Yes	No	Yes	?	Yes	Yes	?	Yes	Yes	No	?	GPLv2[23]
Zimbra	Yes	No	Yes	Yes	Yes	Yes	?	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	No	ZPL and proprietary editions[24]
Mail server	Linux/ Unix	Windows	Mac OS	SMTP	POP3	IMAP	JMAP	IMAP IDLE	SMTP over TLS	POP over TLS	IPv6	SSL	DANE	Webmail	ActiveSync	Sieve	Database	Filesystem	Other	IDN/UTF8	License

Authentication

Mail server	SMTP AUTH	POP before SMTP	APOP	File System	Database	LDAP	Native Anti Hammer - Brute-force attack protection	Other
agorum core	Yes	No	No	No	Yes	Yes	?	PLAIN, LOGIN, CRAM-MD5,[25] NTLM
Apache James	Yes	?	?	?	Yes	Yes	?	PLAIN, LOGIN
Axigen	Yes	No	Yes	Yes	No	Yes	No	GSSAPI, CRAM-MD5,[25] DIGEST-MD5,[26] APOP, CLRTXT, LOGIN, PLAIN, LDAP, Internal
CommuniGate Pro	Yes	Yes	Yes	Yes	Yes	Yes	?	Active Directory (LDAP), CLRTXT, CRAM-MD5,[25] DIGEST-MD5,[26] APOP, GSSAPI, NTLM, MSN, SESSIONID, External Authentication Plug-in. Also supports X.509 PKI auth via STARTTLS/SSL
Courier Mail Server	Yes	Yes	Yes	Yes	Yes	Yes	?	Managed by Courier authentication library which can use PAM, Userdb, PostgreSQL(beta), MySQL, LDAP, and EXTERNAL.
Cyrus IMAP	Yes	Yes	Yes	Yes	Yes	Yes	?	Supports X.509 PKI auth via STARTTLS and EXTERNAL. Uses Cyrus SASL authentication library for support for other mechanisms: Berkeley DB, GDBM, or NDBM (sasldb), PAM, MySQL, PostgreSQL, SQLite, LDAP, Active Directory(LDAP), DCE, Kerberos 4 and 5, proxied IMAP auth, getpwent, shadow, SIA, Courier Authdaemon, httpform, APOP and SASL mechanisms: ANONYMOUS, CRAM-MD5,[25] DIGEST-MD5,[26] SCRAM-SHA-1(-PLUS), SCRAM-SHA-224(-PLUS), SCRAM-SHA-256(-PLUS), SCRAM-SHA-384(-PLUS), SCRAM-SHA-512(-PLUS), EXTERNAL, GSSAPI, LOGIN, NTLM, OTP, PASSDSS, PLAIN, SRP
Dovecot	Yes	Yes	Yes	Yes	Yes	Yes	?	Submission service supports SMTP AUTH.[6] Offers SASL to MTAs.[27][28] POP-before-SMTP via DRAC plugin. PAM, MySQL, PostgreSQL, SQLite, LDAP, Active Directory(LDAP), Kerberos 5, proxied IMAP auth, getpwent, shadow, SIA, BSDauth, Vpopmail. APOP and SASL mechanisms: ANONYMOUS, PLAIN, LOGIN, CRAM-MD5,[25] DIGEST-MD5,[26] SCRAM-SHA-1, EXTERNAL, GSSAPI, NTLM, OTP, SKEY, RPA.
Eudora Internet Mail Server	Yes	No	Yes	Yes	No	No	Yes	CRAM-MD5,[25] DIGEST-MD5,[26] PLAIN, LOGIN
Exim	Yes	Yes	Yes	Yes	Yes	Yes	?	Cyrus SASL, Dovecot SASL, GNU SASL, CRAM-MD5,[25] Heimdal GSSAPI, PLAIN, LOGIN, SPA
FirstClass	Yes	?	?	Yes	Yes	Yes	?
Gordano Messaging Suite	Yes	Yes	Yes	No	Yes	Yes	?	PLAIN, LOGIN, CRAM-MD5,[25] DIGEST-MD5,[26] APOP, ODBC, Active Directory, NT Domain
GroupWise	Yes	Yes	Yes	Yes	Yes	Yes	?	eDirectory, Any LDAPv3-compliant source
Halon	Yes	No	No	Yes	Yes	Yes	?	Many mechanism (SMTP callout, Dovecot SASL, REST, etc.) via script.[29]
Haraka	Yes	No	No	Yes	Yes	Yes	?	Proxy to other server, any other mechanism via AUTH plugins.
IceWarp Mail Server	Yes	Yes	Yes	Yes	Yes	Yes	?	PLAIN, LOGIN, CRAM-MD5,[25] NTLM
Ipswitch IMail Server	Yes	No	Yes	Yes	Yes	Yes	Yes	Active Directory, Windows authentication, CRAM-MD5,[25] PLAIN, LOGIN
Kolab	Yes	Yes	Yes	Yes	Yes	Yes	?	Kolab employs Cyrus and Postfix and thus supports all Cyrus SASL authentication methods and X.509 PKI auth via STARTTLS and EXTERNAL.
Mailsite	Yes	No	Yes	Yes	Yes	Yes	?	NT Domain, Active Directory, PLAIN, LOGIN, NTLM, SCRAM-MD5, CRAM-MD5[25]
Mailtraq	Yes	Yes	Yes	Yes	Yes	Yes	?	NT Domain, Active Directory, Local Directory
MDaemon	Yes	No	Yes	No	No	Yes	Yes
Mercury Mail Transport System	Yes	Yes	Yes	Yes	No	?	?	Internal, LOGIN, PLAIN, CRAM-MD5,[25] Netware, LDAP?, partial NT Domain
Microsoft Exchange Server	Yes	?	Yes	No	No	Yes	Yes	Active Directory, LOGIN,[30] NTLM
NetMail	Yes	Yes	Yes	Yes	Yes	Yes	?	eDirectory, LDAP
Oracle Communications Messaging Server	Yes	Yes	Yes	Yes	Yes	Yes	?	Plain, Login, CRAM-MD5,[25] DIGEST-MD5,[26] Certificate
OpenSMTPD	Yes	No	No	Yes	Yes	Yes	?	By default PLAIN and LOGIN over SSL only, Certificates, bsd_auth and PAM. Supports adding new authentication mechanisms through custom backends.
Postfix	Yes	No	No	Yes	Yes	Yes	Yes	Supports all Cyrus SASL authentication methods except for APOP.
Qpopper	No	Yes	Yes	Yes	Yes	Yes	?	Pluggable Authentication Modules, GSSAPI, CRAM-MD5,[25] DIGEST-MD5,[26] APOP, PLAIN, LDAP, CMU SASL library, Kerberos
qmail	with patch	with vpopmail	Yes	Yes	Yes	Yes	?	Works with any checkpassword utility. The original supports only LOGIN and PLAIN. Alternate checkpassword utilities support authentication against PAM, LDAP, and databases.
Scalix	Yes	?	Yes	Yes	Yes	Yes	?	Internal, LOGIN, PLAIN, X.500 (DAP), LDAP, OpenLDAP, Active Directory, eDirectory, Kerberos, etc.
Sendmail	Yes	Yes	No	Yes	Yes	Yes	?	Supports all Cyrus SASL authentication methods except for APOP. Also supports X.509 PKI auth via STARTTLS and EXTERNAL.
WinGate	Yes	Yes	Yes	Yes	Yes	No	?	NT Domain, Active Directory, CRAM-MD5,[25] SASL PLAIN, SASL LOGIN
Zarafa	Yes	No	No	Yes	Yes	Yes	?	PLAIN, LOGIN using internal backends: Internal, Active Directory, any LDAP-compatible source, Unix
Zentyal	Yes	Yes	Yes	Yes	Yes	Yes	?	Active Directory using Dovecot SASL mechanisms
Zimbra	Yes	No	Yes	Yes	Yes	Yes	?	Internal, LDAP, Open LDAP, Active Directory
Mail server	SMTP AUTH	POP before SMTP	APOP	File System	Database	LDAP	Native Anti Hammer - Brute-force attack protection	Other

Antispam features

Mail Server	DNSBL	SURBL	Spamtraps	Greylisting	SPF	DKIM	DMARC	Tarpit	Bayesian filters	Regular expressions	Embedded Antivirus	Embedded Antispam
agorum core	No	No	No	No	No	No	No	No	No	Yes	No	No
Apache James	?	?	?	?	?	?	?	?	Yes	?	Yes ClamAV[31]	Optional (Apache SpamAssassin)
Axigen	Yes	Yes[32]	Yes	Yes	Yes	Yes	?	No	Yes, in SpamAssassin	Yes	Yes CYREN	Yes CYREN
Citadel	Yes	Yes	No	No	Optional (via SpamAssassin)	?	?	No	Optional (via SpamAssassin)	No	Optional (ClamAV)	Optional (SpamAssassin)
Courier Mail Server	Yes	?	Yes	Yes[33]	Yes	Yes[34]	Yes[35]	Yes	Yes[33]	Yes[33]	Yes Clamav	Yes[33]
Dovecot	?	?	?	?	?	?	?	?	?	?	?	?
Eudora Internet Mail Server	Yes	?	Yes	Yes	?	?	?	?	?	?	?	?
Exim	Yes	Yes	Yes	Yes	Optional at build time	Yes	Optional at build time	Yes	Optional with spamassassin etc.	Yes	Optional any	Optional any
FirstClass	Yes	Yes	No	?	Yes	?	?	Yes	Yes	Yes	Yes Symantec	?
Gordano Messaging Suite	Yes	Yes	Yes	Yes	Yes	?	?	Yes	Yes	Yes	Yes CYREN, Authentium	Yes CYREN
GroupWise	Yes	?	?	?	?	?	?	?	?	?	?	?
Halon	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Optional (via SpamAssassin)	Yes	Optional (Sophos, ClamAV)	Optional (CYREN, SpamAssassin)
Haraka	Yes	Yes	Yes	Yes	Yes	Yes	?	Yes	Optional with spamassassin etc.	Yes	Optional ClamAV, AVG, any via plugins	Optional SpamAssassin, MessageSniffer
hMailServer	Yes	Yes	No	Yes	Yes	Yes	?	No	No	Yes	Yes ClamAV	Yes SpamAssassin
IBM Notes	Yes[36]	?	?	?	No[37]	?	?	?	?	?	?	?
IceWarp Mail Server	Yes	Yes	Yes	Yes	Yes	?	?	Yes	Yes	Yes	Yes	Yes
Ipswitch IMail Server	Yes	Yes	No	No	Yes	Yes[38]	Yes[39]	No	Yes	Yes	Yes Symantec, BitDefender	Yes CYREN
Kolab	Yes	?	?	Yes	Yes	?	?	?	Optional with spamassassin etc.	Yes	Optional (via content filter interface)	Optional (via content filter interface)
Mailsite	Yes	Yes	Yes	Yes	Yes	?	?	No	Yes	Yes	Yes	Yes
Mailtraq	?	?	?	?	?	?	?	?	?	?	?	?
MDaemon	Yes	Yes (via SpamAssassin)	Yes	Yes	Yes	Yes	Yes	Yes	Yes (via SpamAssassin)	Yes (via Content Filter)	Optional Cyren, ClamAV	Yes SpamAssassin
Mercury Mail Transport System	Yes	?	?	Yes (GreyWall extension)	?	?	?	?	Yes (SpamHalter extension)	?	Yes (ClamWall extension)	?
Microsoft Exchange Server	Yes (2003 & later)	?	?	Yes	Yes	Optional (Signing only via 3rd Party Extensions)	?	Yes (2003 & later)	?	?	?	?
NetMail	?	?	?	?	?	?	?	?	?	?	?	?
OpenSMTPD	?	?	?	?	Yes	Yes[40]	?	?	?	?	?	?
Oracle Communications Messaging Server	Yes	Yes	Yes	Yes	Yes	?	?	Yes	Optional with spamassassin etc.	Yes	Optional any	Optional any
Postfix	Yes	?	?	Yes	Yes	Optional[41]	Optional[42]	?	Optional with spamassassin etc.	Yes	Optional (via content filter interface)	Optional (via content filter interface)
qmail	?	?	?	Yes	?	?	?	?	No	?	No	No
Scalix	Yes	Yes (via Scalix AntiSpam powered by Cyren or SpamAssassin)	Yes (via Scalix AntiSpam powered by Cyren or SpamAssassin)	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes (via Scalix ZeroHour AntiVirus powered by Cyren or ClamAV)	Yes
Sendmail	Yes	Yes (via milter/SA)	?	Yes	Optional	Optional[41]	Optional[42]	?	Optional with spamassassin etc.	Yes	Yes ClamAV	Yes SpamAssassin
SparkEngine	?	?	?	?	?	?	?	?	?	?	?	?
UW IMAP	?	?	?	?	?	?	?	?	?	?	?	?
WinGate	?	?	?	?	?	?	?	?	?	?	?	?
Zarafa	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]	External[13]
Zimbra	Yes	Yes (via SpamAssassin)	?	Yes (via Cluebringer Policy Daemon)	Yes	Yes	?	Yes	Yes	Yes (partially)	Yes (via ClamAV, optionally any via Amavisd)	Yes (via SpamAssassin)
Mail Server	DNSBL	SURBL	Spamtraps	Greylisting	SPF	DKIM	DMARC	Tarpit	Bayesian filters	Regular expressions	Embedded Antivirus	Embedded Antispam

See also

• Comparison of email clients
• List of email archive software
• List of mail server software

References

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32. via Kaspersky anti-spam add-on
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35. With zdkimfilter
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41. "OpenDKIM". www.opendkim.org.
42. "Trusted Domain Project - About Us". www.trusteddomain.org.