Comparison of mail servers
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 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.
Authentication
| Mail server | Other | |||||||
| agorum core | PLAIN, LOGIN, CRAM-MD5, NTLM | |||||||
| Apache James | PLAIN, LOGIN | |||||||
| Axigen | GSSAPI, CRAM-MD5, DIGEST-MD5, APOP, CLRTXT, LOGIN, PLAIN, LDAP, Internal | |||||||
| CommuniGate Pro | Active Directory, 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 which can use PAM, Userdb, PostgreSQL, 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, PAM, MySQL, PostgreSQL, SQLite, LDAP, Active Directory, 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, 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 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. | |||||||
| 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 | |||||||
| 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,, 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, 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. | |||||||
| 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 |