Comparison of mail servers

Last updated

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

Contents

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 to enhance or replace the respective system's native MTA.

Microsoft Windows servers do not natively implement e-mail, thus Windows-based MTAs have to supply all the necessary aspects of e-mail-related functionality.

Feature comparison

OS supportProtocol supportFeaturesStorage License
Mail server Linux/Unix Windows macOS SMTP POP3 IMAP JMAP IDLE SMTPS POP3S IPv6 SSL DANE Webmail ActiveSync Sieve IDN/UTF8 Database File-based
agorum core YesYesNoYesNoYesNoNoNoNoNoYesNoYesNoNo?YesNo GPLv2
Apache James YesYesYesYesYesYesYesYesYesYes?Yes?NoNoYes?YesYes ASLv2
Axigen YesYesNoYesYesYes?YesYesYesYesYes?Ajax, Basic & MobileYesYesYesEmbedded, Optimized for Email & GroupwareYes Proprietary (free version: 5 domains, 5 users, 5 groups)
Citadel YesNoYesYesYesYes?NoYesYesYesYes?YesNoYes?YesNo GPLv3
CommuniGate Pro YesYesYesYesYesYes?YesYesYesYesYes?YesYes?YesYesYes Proprietary (Free for up to 5 users)
Courier Mail Server YesNoYesYesYesYes?YesYesYesYesYesNoYesNo maildrop YesNo maildir GPLv3+ [2]
Cyrus IMAP YesNoYesNoYesYesYesYesNoYesYesYesNoNoNoYesNo [3] Indexes onlyYes BSD 4-clause [4]
DBMailYesNoYesNoYesYesNoYesNoYesYesYesNoNoNoNoYesYesNo GPLv2
Dovecot Yes [5] NoYesYes [6] YesYesNoYesYesYesYesYesNoNoNoYesNoYes maildir, mbox, dbox, mdbox, obox [7] Mixed: MIT and LGPL-2.1 [8]
Eudora Internet Mail Server NoNoYesYesYesYes??NoNo?No?NoNo??NoNo Proprietary
Exim YesYes (via Cygwin)YesYesNoNo?NoYesNoYesYesYes [9] NoNoYesYesYesYes GPLv2+ [10]
FirstClass YesYesYesYesYesYes??YesYes?Yes?YesYes??YesYes Proprietary
Gordano Messaging Suite YesYesNoYesYesYes?YesYesYes?Yes?YesYesNo?YesYes Proprietary
GroupWise YesYesNoYesYesYes??YesYes?Yes?YesYes??YesNo Proprietary
HalonYesNoNoYesNoNo?NoYesNoYesYesYes [11] NoNo?YesYesYes Proprietary
Haraka YesYesYesYesNoNo?NoYesNoYesYes?NoNo?YesYesYes MIT
hMailServer NoYesNoYesYesYes?YesYesYesYesYes?YesNo?NoYesYes GNU AGPL
HCL Domino YesYesNoYesYesYesNoNoYesYesYesYesNoYesYes [12] NoYesYesNo Proprietary
IceWarp Mail Server YesYesYesYesYesYes?YesYesYesYesYesNoYesYesNo?YesYes Proprietary
Ipswitch IMail Server NoYesNoYesYesYes?Yes (since v12.2) [13] YesYes?Yes?YesYes??NoYes Proprietary
Kerio Connect YesYesYesYesYesYes?YesYesYesYesYes?YesYesYes?NoYes Proprietary
Kolab YesNoNoYesYesYes?YesYesYesYesYesYesYesYesYes?YesYes GPLv3
Kopano YesNoNopostfix, etc. [14] YesYesNoYespostfixYesYesYespostfixYesz-pushNoYesSQLYes AGPLv3, paid [15]
KumoMTAYesNoNoYesNoNo?NoYesNoYesYesYesNoNo Lua YesYesYes ASLv2
Mailsite NoYesNoYesYesYes??YesYes?Yes?YesYesYes?YesYes Proprietary
MailtraqNoYesNoYesYesYes?YesYesYes?Yes?YesNo??YesYes Proprietary
MDaemon NoYesNoYesYesYes?YesYesYesYesYesNoYesYesNoNot IMAPNoYes Proprietary
Mercury Mail Transport System NoYesNoYesYesYes?YesYesYesNoYesNoYesNoNoNoNoYesProprietary donationware
Microsoft Exchange Server NoYesNoYesYesYesNoYes [16] [17] YesYesYes [18] YesNoYesYes3rd Party supportNot IMAPYesYes Proprietary
NetMail YesYesNoYesYesYes??YesYes?Yes?YesNo??YesNo Proprietary
OpenSMTPD YesNoYesYesNoNoNoNoYesNoYesYesNo [19] NoNoNoNovia custom backendsYes ISC
Open-Xchange YesNoNoYesYesYes??YesYes?Yes?YesYes??YesNoProprietary/SaaS, with open-source parts [20]
Oracle Communications Messaging Server YesNoNoYesYesYes??YesYes?Yes?YesNo?YesYesYes Proprietary
Postfix YesNoYesYesNoNo?NoYesNoYesYesYesNoNoNoYesYesYes IBM Public License
qmail YesNoYesYesYesNo?NoNoNovia QsmtpNoNoNoNo??(cdb)Yes Public domain
Qpopper YesYes (via Cygwin)YesNoYesNo?NoNoYes?Yes?NoNo??NoYes BSD-style (GPL-incompatible) [21]
Scalix YesNoNoYesYesYes?YesYes (via Stunnel)Yes (via Stunnel)?Yes (via Stunnel)?YesYes??YesYes Proprietary with OSS parts, a community (Freeware) and 3 paid editions (SMB, Enterprise, Hosting)
Sendmail YesNoYesYesNoNo?NoYesNoYesYesYes (since 8.16) [22] NoNoNoYes?Yes Sendmail License
SparkEngine YesYesYesYesNoNo?NoYesNo?Yes?NoNo??YesYes Proprietary
UW IMAP YesYesYesNoYesYes?YesNoYesYesYesNo WebPine NoNo?Yes (Indexes)Yes Apache License 2.0 [23]
WinGate NoYesNoYesYesYes?YesYesYesNoYes?YesNo??NoYes Proprietary
Zarafa YesNoNopostfix etc. [14] YesYesNoYespostfixYesYesYespostfixYesz-pushNoNoSQLYes AGPLv3, paid [15]
Zentyal YesNoNoYesYesYes?YesYesYesNoYes?YesYes??YesYesProprietary, 45-day trial
Zimbra YesNoYesYesYesYes?YesYesYesYesYesYesYesYesYesNoYesYes ZPL and proprietary editions [24]
Mail server Linux/Unix Windows macOS SMTP POP3 IMAP JMAP IDLE SMTPS POP3S IPv6 SSL DANE Webmail ActiveSync Sieve IDN/UTF8 Database File-based License

Authentication

Mail server SMTP AUTH POP before SMTP APOP File System Database LDAP Native Anti Hammer - Brute-force attack protectionOther
agorum core YesNoNoNoYesYes?PLAIN, LOGIN, CRAM-MD5, [25] NTLM
Apache James Yes???YesYes?PLAIN, LOGIN
Axigen YesNoYesYesNoYesNoGSSAPI, CRAM-MD5, [25] DIGEST-MD5, [26] APOP, CLRTXT, LOGIN, PLAIN, LDAP, Internal
CommuniGate Pro YesYesYesYesYesYes?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 YesYesYesYesYesYes?Managed by Courier authentication library which can use PAM, Userdb, PostgreSQL(beta), MySQL, LDAP, and EXTERNAL.
Cyrus IMAP YesYesYesYesYesYes?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
DBMailNoNoNoNoYesYesNoLOGIN, Active Directory, OpenLDAP
Dovecot YesYesYesYesYesYes?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 YesNoYesYesNoNoYes CRAM-MD5, [25] DIGEST-MD5, [26] PLAIN, LOGIN
Exim YesYesYesYesYesYes?Cyrus SASL, Dovecot SASL, GNU SASL, CRAM-MD5, [25] Heimdal GSSAPI, PLAIN, LOGIN, SPA
FirstClass Yes??YesYesYes?
Gordano Messaging Suite YesYesYesNoYesYes?PLAIN, LOGIN, CRAM-MD5, [25] DIGEST-MD5, [26] APOP, ODBC, Active Directory, NT Domain
GroupWise YesYesYesYesYesYes? eDirectory, Any LDAPv3-compliant source
HalonYesNoNoYesYesYes?Many mechanism (SMTP callout, Dovecot SASL, REST, etc.) via script. [29]
Haraka YesNoNoYesYesYes?Proxy to other server, any other mechanism via AUTH plugins.
IceWarp Mail Server YesYesYesYesYesYes?PLAIN, LOGIN, CRAM-MD5, [25] NTLM
Ipswitch IMail Server YesNoYesYesYesYesYesActive Directory, Windows authentication, CRAM-MD5, [25] PLAIN, LOGIN
Kolab YesYesYesYesYesYes?Kolab employs Cyrus and Postfix and thus supports all Cyrus SASL authentication methods and X.509 PKI auth via STARTTLS and EXTERNAL.
Mailsite YesNoYesYesYesYes?NT Domain, Active Directory, PLAIN, LOGIN, NTLM, SCRAM-MD5, CRAM-MD5 [25]
MailtraqYesYesYesYesYesYes?NT Domain, Active Directory, Local Directory
MDaemon YesNoYesNoNoYesYes
Mercury Mail Transport System YesYesYesYesNo??Internal, LOGIN, PLAIN, CRAM-MD5, [25] Netware, LDAP?, partial NT Domain
Microsoft Exchange Server Yes?YesNoNoYesYesActive Directory, LOGIN, [30] NTLM
NetMail YesYesYesYesYesYes?eDirectory, LDAP
Oracle Communications Messaging Server YesYesYesYesYesYes?Plain, Login, CRAM-MD5, [25] DIGEST-MD5, [26] Certificate
OpenSMTPD YesNoNoYesYesYesNoBy default PLAIN and LOGIN over SSL only, Certificates, bsd_auth and PAM. Supports adding new authentication mechanisms through custom backends.
Postfix YesNoNoYesYesYesYesSupports all Cyrus SASL authentication methods except for APOP.
Qpopper NoYesYesYesYesYes? Pluggable Authentication Modules, GSSAPI, CRAM-MD5, [25] DIGEST-MD5, [26] APOP, PLAIN, LDAP, CMU SASL library, Kerberos
qmail with patchwith vpopmailYesYesYesYes?Works with any checkpassword utility. The original supports only LOGIN and PLAIN. Alternate checkpassword utilities support authentication against PAM, LDAP, and databases.
Scalix Yes?YesYesYesYes?Internal, LOGIN, PLAIN, X.500 (DAP), LDAP, OpenLDAP, Active Directory, eDirectory, Kerberos, etc.
Sendmail YesYesNoYesYesYes?Supports all Cyrus SASL authentication methods except for APOP. Also supports X.509 PKI auth via STARTTLS and EXTERNAL.
WinGate YesYesYesYesYesNo?NT Domain, Active Directory, CRAM-MD5, [25] SASL PLAIN, SASL LOGIN
Zarafa YesNoNoYesYesYes?PLAIN, LOGIN using internal backends: Internal, Active Directory, any LDAP-compatible source, Unix
Zentyal YesYesYesYesYesYes?Active Directory using Dovecot SASL mechanisms
Zimbra YesNoYesYesYesYes?Internal, LDAP, Open LDAP, Active Directory
Mail server SMTP AUTH POP before SMTP APOP File System Database LDAP Native Anti Hammer - Brute-force attack protectionOther

Antispam features

Mail Server DNSBL SURBL Spamtraps Greylisting SPF DKIM DMARC Tarpit Bayesian filters Regular expressions Embedded Antivirus Embedded Antispam
agorum core NoNoNoNoNoNoNoNoNoYesNoNo
Apache James ????????Yes?Yes ClamAV [31] Optional (Apache SpamAssassin)
Axigen YesNoYesYesYesYes?NoYes, in SpamAssassin YesYes CYREN Yes CYREN
Citadel YesYesNoNoOptional (via SpamAssassin)??NoOptional (via SpamAssassin)NoOptional (ClamAV)Optional (SpamAssassin)
Courier Mail Server Yes?YesYes [32] YesOptional [33] Optional [34] YesYes [32] Yes [32] Yes Clamav Yes [32]
Dovecot No [35] No??????????
Eudora Internet Mail Server Yes?YesYes????????
Exim YesYesYesYesOptional (at build time, most distributions do)Optional (at build time, most distributions do)Optional (at build time, most distributions do)YesOptional with spamassassin etc.YesOptional anyOptional any
FirstClass YesYesNo?Yes??YesYesYesYes Symantec ?
Gordano Messaging Suite YesYesYesYesYes??YesYesYesYes CYREN, Authentium Yes CYREN
GroupWise Yes???????????
HalonYesYesYesYesYesYesYesYesOptional (via SpamAssassin)YesOptional (Sophos, ClamAV)Optional (CYREN, SpamAssassin)
Haraka YesYesYesYesYesYes?YesOptional with spamassassin etc.YesOptional ClamAV, AVG, any via pluginsOptional SpamAssassin, MessageSniffer
hMailServer YesYesNoYesYesYes?NoNoYesYes ClamAV Yes SpamAssassin
IBM Notes Yes [36] ???No [37] ???????
IceWarp Mail Server YesYesYesYesYes??YesYesYesYesYes
Ipswitch IMail Server YesYesNoNoYesYes [38] Yes [39] NoYesYesYes Symantec, BitDefender Yes CYREN
Kolab Yes??YesYes???Optional with spamassassin etc.YesOptional (via content filter interface)Optional (via content filter interface)
Mailsite YesYesYesYesYes??NoYesYesYesYes
Mailtraq????????????
MDaemon YesYes (via SpamAssassin)YesYesYesYesYesYesYes (via SpamAssassin)Yes (via Content Filter)Optional Cyren, ClamAVYes SpamAssassin
Mercury Mail Transport System Yes??Yes (GreyWall extension)????Yes (SpamHalter extension)?Yes (ClamWall extension)?
Microsoft Exchange Server Yes (2003 & later)??YesYesOptional (Signing only via 3rd Party Extensions)?Yes (2003 & later)????
NetMail ????????????
OpenSMTPD ????YesOptional [40] Optional [41] ?????
Oracle Communications Messaging Server YesYesYesYesYes??YesOptional with spamassassin etc.YesOptional anyOptional any
Postfix Yes??YesYesOptional [42] Optional [43] ?Optional with spamassassin etc.YesOptional (via content filter interface)Optional (via content filter interface)
qmail ???Yes????No?NoNo
Scalix YesYes (via Scalix AntiSpam powered by Cyren or SpamAssassin)Yes (via Scalix AntiSpam powered by Cyren or SpamAssassin)YesYesYesYesYesYesYesYes (via Scalix ZeroHour AntiVirus powered by Cyren or ClamAV)Yes
Sendmail YesYes (via milter/SA)?YesOptionalOptional [42] Optional [43] ?Optional with spamassassin etc.YesYes ClamAV Yes SpamAssassin
SparkEngine ????????????
UW IMAP ????????????
WinGate ????????????
Zarafa External [14] External [14] External [14] External [14] External [14] External [14] External [14] External [14] External [14] External [14] External [14] External [14]
Zimbra YesYes (via SpamAssassin)?Yes (via Cluebringer Policy Daemon)YesYes?YesYesYes (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

Related Research Articles

The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typically use SMTP only for sending messages to a mail server for relaying, and typically submit outgoing email to the mail server on port 587 or 465 per RFC 8314. For retrieving messages, IMAP is standard, but proprietary servers also often implement proprietary protocols, e.g., Exchange ActiveSync.

<span class="mw-page-title-main">Maildir</span> E-mail format

The Maildir e-mail format is a common way of storing email messages on a file system, rather than in a database. Each message is assigned a file with a unique name, and each mail folder is a file system directory containing these files. Maildir was designed by Daniel J. Bernstein circa 1995, with a major goal of eliminating the need for program code to handle file locking and unlocking through use of the local filesystem.

<span class="mw-page-title-main">Exim</span> Mail transfer agent (written 1995)

Exim is a mail transfer agent (MTA) used on Unix-like operating systems. Exim is a free software distributed under the terms of the GNU General Public License, and it aims to be a general and flexible mailer with extensive facilities for checking incoming e-mail.

A message delivery agent (MDA), or mail delivery agent, is a computer software component that is responsible for the delivery of e-mail messages to a local recipient's mailbox. It is also called a local delivery agent (LDA).

<span class="mw-page-title-main">GNU Mailman</span> Mailing list manager software

GNU Mailman is a computer software application from the GNU Project for managing electronic mailing lists. Mailman is coded primarily in Python and currently maintained by Abhilash Raj. Mailman is free software, licensed under the GNU General Public License.

Messaging Application Programming Interface (MAPI) is an API for Microsoft Windows which allows programs to become email-aware. While MAPI is designed to be independent of the protocol, it is usually used to communicate with Microsoft Exchange Server.

<span class="mw-page-title-main">Pegasus Mail</span> Proprietary email client

Pegasus Mail is a proprietary email client for Microsoft Windows. It was originally released in 1990 on NetWare networks with MS-DOS and later Apple Macintosh clients, before being ported to Windows which is now the only platform actively supported. Since its inception it has been developed by David Harris and is donationware after having previously been freeware.

<span class="mw-page-title-main">Postfix (software)</span> Mail transfer agent

Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail.

The Cyrus IMAP server is electronic mail server software developed by Carnegie Mellon University. It differs from other Internet Message Access Protocol (IMAP) server implementations in that it is generally intended to be run on sealed servers, where normal users cannot log in.

<span class="mw-page-title-main">Dovecot (software)</span>

Dovecot is an open-source IMAP and POP3 server for Unix-like operating systems, written primarily with security in mind. Timo Sirainen originated Dovecot and first released it in July 2002. Dovecot developers primarily aim to produce a lightweight, fast and easy-to-set-up open-source email server.

The UW IMAP server was the reference server implementation of the Internet Message Access Protocol. It was developed at the University of Washington by Mark Crispin and others.

Opportunistic TLS refers to extensions in plain text communication protocols, which offer a way to upgrade a plain text connection to an encrypted connection instead of using a separate port for encrypted communication. Several protocols use a command named "STARTTLS" for this purpose. It is a form of opportunistic encryption and is primarily intended as a countermeasure to passive monitoring.

Bynari is a defunct company based in Dallas, developing server and email software, mainly known for its Insight Family, similar to Microsoft Exchange Server with Outlook.

The Courier Mail Server is a mail transfer agent (MTA) server that provides SMTP, IMAP, POP3, SMAP, webmail, and mailing list services with individual components. It is best known for its IMAP server component.

<span class="mw-page-title-main">Email agent (infrastructure)</span>

An e-mail agent is a program that is part of the e-mail infrastructure, from composition by sender, to transfer across the network, to viewing by recipient. The best-known are message user agents and message transfer agents, but finer divisions exist.

Ipswitch IMail Server is an email server application with groupware functionality that runs on Microsoft Windows OS. It was developed in 1994 by Ipswitch, Inc., a software company based in Lexington, Massachusetts.

MailEnable is a Windows-based, commercial email server distributed by MailEnable Pty. Ltd, an Australian-based software company which was established in 2002.

Kopano is an open-source groupware application suite originally based on Zarafa. The initial version of Kopano Core (KC) was forked from the then-current release of Zarafa Collaboration Platform, and superseded ZCP in terms of lineage as ZCP switched to maintenance mode with patches flowing from KC. Kopano WebApp similarly descended from Zarafa WebApp. Since October 2017, Kopano Core is also known more specifically as Kopano Groupware Core, since Kopano B.V. developed more products that were not directly requiring groupware components.

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