Comparison of mail servers

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This is a comparison of mail servers: 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.

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

Feature comparison[edit]

Server OS support Features Storage Users
Mail server Linux/Unix SMTP POP3 IMAP IMAP IDLE SMTP over TLS DANE POP over TLS IPv6 SSL Webmail ActiveSync Sieve Database Filesystem Other License
agorum core Yes Yes No Yes No No No No No Yes Yes No No Yes No No GPLv2
Apache James Yes Yes Yes Yes Yes Yes ? Yes ? Yes No No Yes Yes Yes No ASLv2
Axigen Yes Yes Yes Yes Yes Yes ? Yes Yes Yes Ajax, Basic & Mobile Yes Yes Proprietary, Embedded, Optimized for Email and Groupware No Yes Proprietary (free version: 5 domains, 5 users, 5 groups)
Citadel 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 Proprietary (Free for up to 5 users)
Courier Mail Server Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes No maildrop No maildir No GPLv3[2]
Cyrus IMAP Yes No Yes Yes Yes No ? Yes Yes Yes No No Yes Yes (indexes) Yes Yes 4-clause BSD[3]
Dovecot Yes[4] No Yes Yes Yes No ? Yes Yes Yes No No Yes Yes maildir, mbox, dbox No Mixed: MIT and LGPL 2.1[5]
Eudora Internet Mail Server No Yes Yes Yes ? No ? No ? No No No ? No No Yes Proprietary
Exim Yes Yes Dovecot, UW IMAP Dovecot, UW IMAP Dovecot, UW IMAP Yes Yes[6] No Yes Yes No No Yes Yes Yes No GPLv2+[7]
FirstClass Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes Yes ? Yes Yes Yes Proprietary
Gordano Messaging Suite Yes Yes Yes Yes Yes Yes ? Yes ? Yes Yes Yes No Yes Yes Yes Proprietary
GroupWise Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes Yes ? Yes No No Proprietary
Halon Yes Yes No No No Yes Yes[8] No Yes Yes No No ? Yes Yes Yes Proprietary
Haraka Yes Yes No No No Yes ? No Yes Yes No No ? Yes Yes Yes MIT
hMailServer No Yes Yes Yes Yes Yes ? Yes Yes Yes Yes No ? Yes Yes No GNU AGPL
IBM Lotus Domino Yes Yes Yes Yes ? Yes ? Yes Yes Yes Yes Yes ? Yes No No Proprietary
IceWarp Mail Server Yes Yes Yes Yes Yes Yes ? Yes Yes Yes Yes Yes ? Yes Yes No Proprietary
Ipswitch IMail Server No Yes Yes Yes Yes (since v12.2)[9] Yes ? Yes ? Yes Yes Yes ? No Yes No Proprietary
Kerio Connect Yes Yes Yes Yes Yes Yes ? Yes Yes Yes Yes Yes Yes No Yes No Proprietary
Kolab Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes GPLv3
Kopano Yes External[10] Yes Yes Yes External[10] No Yes Yes Yes Yes Yes No Yes Yes Amazon S3 AGPLv3, paid[11]
Mailsite No Yes Yes Yes ? Yes ? Yes ? Yes Yes Yes Yes Yes Yes Yes Proprietary
Mailtraq No Yes Yes Yes Yes Yes ? Yes ? Yes Yes No ? Yes Yes Yes Proprietary
MDaemon No Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes No No Yes Yes Proprietary
Mercury Mail Transport System No Yes Yes Yes Yes Yes ? Yes ? Yes Yes No ? No Yes No Proprietary donationware
Microsoft Exchange Server No Yes Yes Yes Yes[12][13] Yes ? Yes Yes (2007 sp1 onwards)[14] Yes Yes Yes ? ESE only Yes (up to 2003 only)[15] Yes Proprietary
NetMail Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes No ? Yes No No Proprietary
OpenSMTPD Yes Yes No No No Yes No[16] No Yes Yes No No ? possible through custom backends Yes No ISC
Open-Xchange Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes Yes ? Yes No No Proprietary/SaaS, with open-source parts[17]
Oracle Communications Messaging Server Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes No ? Yes Yes No Proprietary
Postfix Yes Yes Dovecot, UW IMAP Dovecot, UW IMAP Dovecot, UW IMAP Yes Yes No Yes Yes No No No Yes Yes Yes IBM Public License
qmail Yes Yes Yes Dovecot, UW IMAP Dovecot, UW IMAP No No Dovecot, UW IMAP via Qsmtp No No No ? (cdb) Yes No Public domain
Qpopper Yes No Yes No No No ? Yes ? Yes No No ? No Yes Yes BSD-style, GPL-incompatible[18]
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 Yes Dovecot, UW IMAP Dovecot, UW IMAP Dovecot, UW IMAP Yes ? No Yes Yes No No No ? Yes ? Sendmail License
SparkEngine Yes Yes No No No Yes ? No ? Yes No No ? Yes Yes Yes Proprietary
Synovel Collabsuite Yes Yes Yes Yes ? Yes ? Yes ? Yes Yes No ? Yes Yes ? Proprietary with OSS parts, Freeware and paid editions[19]
UW IMAP Yes No Yes Yes Yes No No Yes Yes Yes WebPine No No Yes (Indexes) Yes No Apache License 2.0[20]
WinGate No Yes Yes Yes Yes Yes ? Yes No Yes Yes No ? No Yes No Proprietary
Zarafa Yes External[10] Yes Yes Yes External[10] No Yes Yes Yes Yes Yes No Yes Yes No AGPLv3, paid[11]
Zentyal Yes Yes Yes Yes Yes Yes ? Yes No Yes Yes Yes ? Yes Yes No GPLv2[21]
Zimbra Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No ZPL and proprietary editions[22]
Mail server Linux/Unix SMTP POP3 IMAP IMAP IDLE SMTP over TLS DANE POP over TLS IPv6 SSL Webmail ActiveSync Sieve Database Filesystem Other License

Authentication[edit]

Mail server SMTP AUTH POP before SMTP APOP Filesystem Database LDAP Other
agorum core Yes No No No Yes Yes PLAIN, LOGIN, CRAM-MD5, NTLM
Apache James Yes ? ? ? Yes Yes PLAIN, LOGIN
Axigen Yes No Yes No No Yes GSSAPI, CRAM-MD5, DIGEST-MD5, APOP, CLRTXT, LOGIN, PLAIN, LDAP, Internal
CommuniGate Pro Yes Yes Yes Yes Yes Yes Active Directory (LDAP), CLRTXT, CRAM-MD5, DIGEST-MD5, 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 No 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, DIGEST-MD5, EXTERNAL, GSSAPI, LOGIN, NTLM, OTP, PASSDSS, PLAIN, SRP
Dovecot No Yes Yes Yes Yes Yes Not an SMTP server, but offers SASL to MTAs.[23][24] 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, DIGEST-MD5, SCRAM-SHA1, EXTERNAL, GSSAPI, NTLM, OTP, SKEY, RPA.
Eudora Internet Mail Server Yes No Yes Yes No No CRAM-MD5, DIGEST-MD5, PLAIN, LOGIN
Exim Yes Yes Yes Yes Yes Yes Cyrus SASL, Dovecot SASL, GNU SASL, CRAM-MD5, Heimdal GSSAPI, PLAIN, LOGIN, SPA
FirstClass Yes ? ? Yes Yes Yes
Gordano Messaging Suite Yes Yes Yes No Yes Yes PLAIN, LOGIN, CRAM-MD5, DIGEST-MD5, 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.[25]
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, NTLM
Ipswitch IMail Server Yes No Yes Yes Yes Yes Active Directory, Windows authentication, CRAM-MD5, 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
Mailtraq Yes Yes Yes Yes Yes Yes NT Domain, Active Directory, Local Directory
Mercury Mail Transport System Yes Yes Yes Yes No ? Internal, LOGIN, PLAIN, CRAM-MD5, Netware, LDAP?, partial NT Domain
Microsoft Exchange Server Yes ? Yes No No Yes Active Directory, LOGIN,[26] NTLM
NetMail Yes Yes Yes Yes Yes Yes eDirectory, LDAP
Oracle Communications Messaging Server Yes Yes Yes Yes Yes Yes Plain, Login, CRAM-MD5, Digest-MD5, 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 Supports all Cyrus SASL authentication methods except for APOP.
Qpopper No Yes Yes Yes Yes Yes Pluggable Authentication Modules, GSSAPI, CRAM-MD5, DIGEST-MD5, 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, 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 Filesystem Database LDAP Other

Antispam features[edit]

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[27] Optional (Apache SpamAssassin)
Axigen Yes Yes[28] No 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[29] Yes Yes[30] Yes[31] Yes Yes[29] Yes[29] Yes Clamav Yes[29]
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 Lotus Domino Yes[32] ? ? ? No[33] ? ? ? ? ? ? ?
IceWarp Mail Server Yes Yes Yes Yes Yes ? ? Yes Yes Yes Yes Yes
Ipswitch IMail Server Yes Yes No No Yes Yes[34] Yes[35] 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 ? ? ? ? ? ? ? ? ? ? ? ?
Mercury Mail Transport System Yes ? ? Yes (GreyWall extension) ? ? ? ? Yes (SpamHalter extension) ? Yes (ClamWall extension) ?
Microsoft Exchange Server Yes (2003 & later) ? ? Yes Yes ? ? Yes (2003 & later) ? ? ? ?
NetMail ? ? ? ? ? ? ? ? ? ? ? ?
OpenSMTPD ? ? ? ? Yes Yes[36] ? ? ? ? ? ?
Oracle Communications Messaging Server Yes Yes Yes Yes Yes ? ? Yes Optional with spamassassin etc. Yes Optional any Optional any
Postfix Yes ? ? Yes Yes Optional[37] Optional[38] ? 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[37] Optional[38] ? Optional with spamassassin etc. ? Yes ClamAV Yes SpamAssassin
SparkEngine ? ? ? ? ? ? ? ? ? ? ? ?
Synovel Collabsuite Yes Yes Yes Yes Yes ? ? ? Yes Yes YesClamAV Yes SpamAssassin
UW IMAP ? ? ? ? ? ? ? ? ? ? ? ?
WinGate ? ? ? ? ? ? ? ? ? ? ? ?
Zarafa External[10] External[10] External[10] External[10] External[10] External[10] External[10] External[10] External[10] External[10] External[10] External[10]
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[edit]

References[edit]

  1. ^ Mahoney, Michael S. "The Unix Oral History Project: Release.0, The Beginning". Mahoney: To me one of the lovely features of pipes is the way it reinforces the notion of toolbox ...
  2. ^ See COPYING file in the distribution
  3. ^ "Archived copy". Archived from the original on 2013-03-12. Retrieved 2013-03-06.
  4. ^ Dovecot Operating System Compatibility. Retrieved on 2008-09-03.
  5. ^ "Dovecot licensing information: COPYING". Retrieved 2008-09-03.
  6. ^ "Exim 4.91 spec: Encrypted SMTP connections using TLS/SSL / 15. DANE". exim.org. Retrieved 2018-07-05.
  7. ^ See NOTICE file in the distribution
  8. ^ "Halon DANE support". Halon Security AB. Retrieved 2015-12-17.[self-published source]
  9. ^ "IMail v12.2 Release Notes". docs.ipswitch.com.
  10. ^ a b c d e f g h i j k l m n o p Zarafa Collaboration Platform architecture diagram. Retrieved on 2011-12-10.
  11. ^ a b "Kopano Pricing - Subscription Plans - Kopano Partners".
  12. ^ Archiveddocs. "Microsoft Exchange Server 2007 RFC and Support for Standards: Exchange 2007 Help". technet.microsoft.com.
  13. ^ Archiveddocs. "Exchange 2010 Support for RFC Standards: Exchange 2010 Help". technet.microsoft.com.
  14. ^ Archiveddocs. "IPv6 Support in Exchange 2007 SP1 and SP2: Exchange 2007 Help". technet.microsoft.com.
  15. ^ Archiveddocs. "NTFS and the Installable File System". msdn.microsoft.com.
  16. ^ "OpenSMTPD, current state of affairs: Lookup layer change" (PDF). OpenBSD.org. Retrieved 2018-07-24.[self-published source]
  17. ^ "Licenses-OX-APP-Suite - Open-Xchange". www.open-xchange.com.
  18. ^ Contains jurisdiction selection and IBM Public License-style indemnification clause.
  19. ^ [1]Comparison of mail servers] Archived 2013-03-01 at the Wayback Machine.
  20. ^ "UW IMAP software--UW IMAP Server Documentation". www.washington.edu.
  21. ^ "Zentyal Linux Small Business Server". www.zentyal.org.
  22. ^ "Licenses and Terms of Use". www.zimbra.com.
  23. ^ "DovecotFeatures - Dovecot Wiki". wiki.dovecot.org.
  24. ^ "Authentication - Dovecot Wiki". wiki.dovecot.org.
  25. ^ "HSL - Halon SMTP server". Halon Security AB. Retrieved 2016-02-11.
  26. ^ "How to Configure Exchange to Allow AUTH LOGIN to work". support2.gwava.com.
  27. ^ "Documentation for build-in ClamAV-Mailet". Retrieved 2013-03-19.
  28. ^ via Kaspersky anti-spam add-on
  29. ^ a b c d "Index of /~gordon/courier-pythonfilter". phantom.dragonsdawn.net.
  30. ^ Two DKIM filters can be found in Courier-MTA's links page
  31. ^ With zdkimfilter
  32. ^ "IBM Gathering DNS Blacklist Filter statistics - United States". www-01.ibm.com. 30 June 2014.
  33. ^ "IBM Does Lotus Domino support Sender Policy Framework (SPF)? - United States". www-01.ibm.com. 5 June 2014.
  34. ^ Inc., Ipswitch,. "IMail Secure Mail Server - Ipswitch". www.imailserver.com.
  35. ^ Inc., Ipswitch,. "Your IMail Software Upgrades and Patches - Ipswitch IMail Server". www.imailserver.com.
  36. ^ Faurot, Eric. "OpenSMTPD: We deliver!". www.opensmtpd.org.
  37. ^ a b "OpenDKIM". www.opendkim.org.
  38. ^ a b "Trusted Domain Project - About Us". www.trusteddomain.org.