Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
AMaViS (A Mail Virus Scanner) scans e-mail attachments for viruses using third-party virus scanners available for UNIX environments. It resides on a UNIX (Linux) machine and looks through the attached files arriving via e-mail, generates reports when a virus is found and sets the delivery on hold.
The Cyrus IMAP server is generally intended to be run on sealed systems, where normal users are not permitted to log in. The mailbox database is stored in parts of the filesystem that are private to Cyrus. All user access to mail is through the IMAP, POP3, or KPOP protocols. The private mailbox database design gives the server large advantages in efficiency, scalability, and administratability. Multiple concurrent read/write connections to the same mailbox are permitted. The server supports access control lists on mailboxes and storage quotas on mailbox hierarchies, multiple SASL mechanisms, and the Sieve mail filtering language.
Iris is a CGI script, Exim MTA and Dovecot configuration files, and Vagrant and Ansible playbook, supplemented with instructions on building an e-mail server with virtual domain support, authenticated SMTP relay, vacation, SMTP-time malware/spam/over-quota reject, and Web based account and domain administration, including domain-level access control for delegated domain management. It is based on Exim MTA, Dovecot IMAP server, MySQL, Perl, Clamav, SpamAssassin, and Roundcube Webmail.
dl is a file exchange service that allows you to upload any file to a Web server and generate a unique ticket for others to download. The ticket is automatically expired according to the specified rules, so that you don't need to keep track or cleanup afterward. dl also allows you to grant an anonymous, one-time upload for others to send you a file, without the requirement of account management. dl is usually installed as a replacement for email attachments due to its simplicity (though it can be used in other ways).
Evolution is the GNOME mailer, calendar, contact manager, and communications tool. Evolution represents the next step forward in GNOME applications. The tools which make up Evolution will be tightly integrated with one another and act as a seamless personal information-management tool.
Dovecot is an IMAP server whose major goals are security and extreme reliability. It uses index files to optimally store the mailbox state, which makes it very fast even with huge mailboxes. Indexes won't prevent external mailbox updates, so Dovecot is still fully compatible with standard Maildir and mbox formats. There's also a fully featured POP3 server included.