Mailismus is a secure high-performance mail server, which incorporates SMTP, IMAP and POP3 servers. It is highly configurable, capable of performing multiple roles and is possibly the fastest single-instance mail server available.
It runs on any Unix/Linux, Windows or MacOS X platform and merely requires Java (Java 8 or later) to be installed.

Features include:

• SMTP message switch
• SMTP Authentication, with SSL and STARTTLS
• IMAP and POP3 mailbox access - with SASL authentication, SSL and STLS
• Massively parallel - supports thousands of concurrent connections
• Greylisting and Blacklisting (anti-spam measures)
• Non-blocking DNS validation (anti-spam measures)
• SPF-compatible email forwarding
• Route SMTP messages by sender or recipient
• POP3 retriever - consolidate emails from multiple providers in one location
• Configurable message-filtering plugins
• Web-enabled management agent - monitor Mailismus from your web browser
• Supports multi-node mailserver infrastructure - unknown users rejected at perimeter nodes, to avoid generating bounce reports at final delivery stage
• Detailed logging - provides trace logs, transcripts and audit logs
• Maildir mailbox storage format
• Highly configurable

See the Admin Guide for the full details.
Mailismus is powered by the Network Application Framework (NAF).

Mailismus is free and open-source, distributed under the terms of the GNU Affero General Public License, version 3 (AGPLv3).
See LICENCE.
See COPYRIGHT.

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Some typical deployment scenarios to which Mailismus is suited are:

• Standard Incoming/Outgoing SMTP Server, with or without local mailboxes:
  Mailismus is designed from the ground up with the scalability, functionality and security to be used as the central corporate or departmental mail server.
  The SMTP switch at its core sends, receives and relays email messages, while the integrated IMAP and POP3 servers provide mailbox access for local users.
  Deploying IMAP rather than POP3 allows mail storage to be decoupled from your email client and your messages can then be accessed from multiple apps and locations, while being centrally stored and backed up.
  
  
• MX backup:
  Mailismus can be configured as a secondary MX relay for one or more email domains.
  Most email domains nominate multiple mail servers via MX records in the DNS and senders connect to them in decreasing order of preference. The highest-priority MX node is the final-destination mail server (ie. the one where the mailboxes actually reside) but lower priority MX nodes allow email for that domain to be accepted even when the primary server is down or overloaded. These secondary nodes then transparently forward the messages to the primary mail server when it is ready.
  
  
• Incoming Distribution Point:
  Although Mailismus itself can act as the ultimate email destination (ie. can host mailboxes) it can also be configured as an Internet-facing fan-out server, which forwards messages for specific domains on to configured mail servers.
  The reasons why you might want to put Mailismus in front of your final-destination mail servers, would probably come down to its speed, anti-spam measures and security.
  In this configuration, Mailismus effectively serves as a fast, secure concentrator.
  
  
• Personal all-in-one mail server:
  The Mailismus POP3 retriever allows you to download your messages from all your ISPs and email providers and consolidate them in one mailbox (per user) on your local Mailismus instance.
  You can then use either or both of the Mailismus POP3 and IMAP servers (according to user preferences) to access your email and manage it locally using your favourite email client (Outlook, Thunderbird, Eudora, etc).
  You can continue to send and receive email via your normal ISP, with the Mailismus SMTP server acting as an outgoing middle-man.
  Running Mailismus as a local SMTP relay on your laptop also allows you to submit emails while offline and Mailismus will deliver them you go online.
  
  

In addition to its performance and anti-spam measures, Mailismus is also distinguished by the depth and breadth of its logging options, providing for formal audit logs and exhaustive SMTP, IMAP and POP3 transcripts, in addition to the standard trace-level application logging you would normally expect.
Never again need you face the frustration of submitting messages into a black hole and wondering what happened to them and why.