The comparison of mail servers covers mail transfer agents (MTAs), 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 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
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 Apache James Axigen (free version: 5 domains, 5 users, 5 groups) Citadel CommuniGate Pro (Free for up to 5 users) Courier Mail Server Cyrus IMAP DBMail Dovecot Dovecot Operating System Compatibility. Retrieved on 2008-09-03. Dovecot Submission Service. Retrieved on 2010-07-15. Eudora Internet Mail Server Exim (via Cygwin) See NOTICE file in the distribution FirstClass Gordano Messaging Suite GroupWise Halon Haraka hMailServer HCL Domino IceWarp Mail Server Ipswitch IMail Server (since v12.2) Kerio Connect Kolab Kopano KumoMTA maddy Mailsite Mailtraq MDaemon Mercury Mail Transport System Microsoft Exchange Server 3rd Party support mox NetMail OpenSMTPD Open-Xchange Oracle Communications Messaging Server Postfix qmail with with patch with , via Qsmtp with with patch Qpopper (via Cygwin) Contains jurisdiction selection and IPL-style indemnification clause. Scalix (via Stunnel) (via Stunnel) (via Stunnel) Sendmail (since 8.16)Sendmail Release Notes. Retrieved on 2021-01-08. SparkEngine Stalwart UW IMAP WebPine (Indexes) WinGate Zarafa Zentyal Zimbra 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 Other agorum core PLAIN, LOGIN, CRAM-MD5,CRAM-MD5 to Historic, 20 November 2008. NTLM Apache James PLAIN, LOGIN Axigen GSSAPI, CRAM-MD5, DIGEST-MD5,Moving DIGEST-MD5 to Historic, July 2011. APOP, CLRTXT, LOGIN, PLAIN, LDAP, Internal CommuniGate Pro 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 Managed by Courier authentication library which can use PAM, Userdb, PostgreSQL(beta), MySQL, LDAP, and EXTERNAL. Cyrus IMAP 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, 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 DBMail LOGIN, Active Directory, OpenLDAP Dovecot Submission service supports SMTP AUTH. Offers SASL to MTAs. 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-SHA-1, EXTERNAL, GSSAPI, NTLM, OTP, SKEY, RPA. Eudora Internet Mail Server CRAM-MD5, DIGEST-MD5, PLAIN, LOGIN Exim Cyrus SASL, Dovecot SASL, GNU SASL, CRAM-MD5, Heimdal GSSAPI, PLAIN, LOGIN, SPA FirstClass Gordano Messaging Suite PLAIN, LOGIN, CRAM-MD5, DIGEST-MD5, APOP, ODBC, Active Directory, NT Domain GroupWise eDirectory, Any LDAPv3-compliant source Halon Many mechanism (SMTP callout, Dovecot SASL, REST, etc.) via script. Haraka Proxy to other server, any other mechanism via AUTH plugins. HCL Domino Passkeys, Time-based one-time password IceWarp Mail Server PLAIN, LOGIN, CRAM-MD5, NTLM Ipswitch IMail Server Active Directory, Windows authentication, CRAM-MD5, PLAIN, LOGIN Kolab Kolab employs Cyrus and Postfix and thus supports all Cyrus SASL authentication methods and X.509 PKI auth via STARTTLS and EXTERNAL. maddy PLAIN, LOGIN Mailsite NT Domain, Active Directory, PLAIN, LOGIN, NTLM, SCRAM-MD5, CRAM-MD5 Mailtraq NT Domain, Active Directory, Local Directory MDaemon Mercury Mail Transport System Internal, LOGIN, PLAIN, CRAM-MD5, Netware, LDAP?, partial NT Domain Microsoft Exchange Server Active Directory, LOGIN, NTLM mox PLAIN, LOGIN, CRAM-MD5, SCRAM-SHA-1, SCRAM-SHA-256 (both with channel binding variants), EXTERNAL NetMail eDirectory, LDAP Oracle Communications Messaging Server Plain, Login, CRAM-MD5, DIGEST-MD5, Certificate OpenSMTPD By default PLAIN and LOGIN over SSL only, Certificates, bsd_auth and PAM. Supports adding new authentication mechanisms through custom backends. Postfix Supports all Cyrus SASL authentication methods except for APOP. Qpopper Pluggable Authentication Modules, GSSAPI, CRAM-MD5, DIGEST-MD5, APOP, PLAIN, LDAP, CMU SASL library, Kerberos qmail Works with any checkpassword utility. The original supports only LOGIN and PLAIN. Alternate checkpassword utilities support authentication against PAM, LDAP, and databases. Scalix Internal, LOGIN, PLAIN, X.500 (DAP), LDAP, OpenLDAP, Active Directory, eDirectory, Kerberos, etc. Sendmail Supports all Cyrus SASL authentication methods except for APOP. Also supports X.509 PKI auth via STARTTLS and EXTERNAL. Stalwart PLAIN, LOGIN, OAUTHBEARER, XOAUTH2; also OAuth 2.0, OpenID Connect and TOTP two-factor authentication WinGate NT Domain, Active Directory, CRAM-MD5, SASL PLAIN, SASL LOGIN Zarafa PLAIN, LOGIN using internal backends: Internal, Active Directory, any LDAP-compatible source, Unix Zentyal Active Directory using Dovecot SASL mechanisms Zimbra Internal, LDAP, Open LDAP, Active Directory Mail server Other Authentication possibilites
Antispam features
Mail Server DNSBL SURBL Spamtraps Greylisting SPF DKIM DMARC Tarpit Bayesian filters Regular expressions Embedded Antivirus Embedded Antispam agorum core Apache James ClamAV (Apache SpamAssassin) Axigen , in SpamAssassin CYREN CYREN Citadel (via SpamAssassin) (via SpamAssassin) (ClamAV) (SpamAssassin) Courier Mail Server Two DKIM filters can be found in Courier-MTA's links page With Clamav Dovecot Considered and rejected by developers in 2013. Eudora Internet Mail Server Exim (at build time, most distributions do) (at build time, most distributions do) (at build time, most distributions do) with spamassassin etc. any any FirstClass Symantec Gordano Messaging Suite CYREN, Authentium CYREN GroupWise Halon (via SpamAssassin) (Sophos, ClamAV) (CYREN, SpamAssassin, Eleven eXpurgate) Haraka with spamassassin etc. ClamAV, AVG, any via plugins SpamAssassin, MessageSnifferHCL Domino with ICAP hMailServer ClamAV SpamAssassin IceWarp Mail Server Ipswitch IMail Server Symantec, BitDefender CYREN Kolab with spamassassin etc. (via content filter interface) (via content filter interface) maddy (via a milter, e.g. ClamAV) (via Rspamd) Mailsite Mailtraq MDaemon (via SpamAssassin) (via SpamAssassin) (via Content Filter) Cyren, ClamAV SpamAssassin Mercury Mail Transport System (GreyWall extension) (SpamHalter extension) (ClamWall extension) Microsoft Exchange Server (2003 & later) (Signing only via 3rd Party Extensions) (2003 & later) mox NetMail OpenSMTPD With or With Oracle Communications Messaging Server with spamassassin etc. any any Postfix (via milter-link) with spamassassin etc. (via content filter interface) (via content filter interface) qmail with patch with patch, with patch, with patch, Scalix (via Scalix AntiSpam powered by Cyren or SpamAssassin) (via Scalix AntiSpam powered by Cyren or SpamAssassin) (via Scalix AntiSpam powered by Cyren or SpamAssassin) (via Scalix AntiSpam powered by Cyren or SpamAssassin) (via Scalix AntiSpam powered by Cyren or SpamAssassin) (via Scalix ZeroHour AntiVirus powered by Cyren or ClamAV) Sendmail (via milter/SA) with spamassassin etc. ClamAV SpamAssassin SparkEngine Stalwart UW IMAP WinGate Zarafa Zimbra (via SpamAssassin) (via Cluebringer Policy Daemon) (partially) (via ClamAV, optionally any via Amavisd) (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