phlyMail is a groupware, webmailer, and PIM. It offers unlimited nested groups, unlimited POP3/IMAP profiles, quotas, an integrated address book, a calendar with multiple reminders and event repetitions, a file manager with an integrated WebDAV server, the ability to send faxes, SMS support (which lets you send SMS, get reminded of events via SMS, and get email notification via SMS), a bookmark manager, themes, and multilingual support. It uses either sendmail or SMTP to send email, and can handle MIME and SSL connections. Support for IDN (Internationalized Domain Names) is included. Through its modular design, it's easy to add completely new features as modules, which can be plugged into the system.
Hastymail is a full featured IMAP/SMTP client written in PHP. The goal is a full featured yet lightweight Web mail client. After a complete review and rewrite, it provides many improvements over the original code including optional AJAX functionality, improved code organization, a plugin API, CSS and PHP template themes, and much more.
IMAPEngine is an IMAP server that uses a tdbengine database structure to store all accounts, messages, and mailboxes. This means it has nearly no limits in numbers, sizes, and performance, and it uses indexes to sort/find its data. IMAPEngine is IMAP4Rev1 compatible and also has built-in support for the ACL, ID, IDLE, and UIDPLUS extensions. It is not (yet) an MTA, but it retrieves incoming messages from different POP3 servers. An simple integrated Web interface makes account configuration easy.
Openmailadmin is a little administration interface to every complete IMAP mail server daemon. It supports every feature IMAP provides, and fits in most MTA configurations. A key feature is the non-standard, generic administration hierarchy which not only seperates "normal users" from "administrators", but enables the mailserver-master to create instances between them. You will be able to let other users create their own sub-users and thus either share a single mail server between different organizations or project your company's employee structure. It excels with features such as regex addresses and folder ACL management.
Kolab is a groupware system that provides a comprehensive and flexible solution for workgroups. Email, contacts, and group calendars can be managed via the Web, Windows/Outlook, and Linux/KDE. It supports offline synchronization and full seamless support of mixed client environments because the Kolab-XML storage format is fully open and avoids MAPI/TNEF.
GROUP-E is collaboration software which integrates groupware, project management, and business server on one platform. The solution is based on a LAMP architecture (Linux, Apache, MySQL, PHP). GROUP-E offers project management, transparent Samba (file server) integration, integration of Cyrus IMAP server with administration and personal SIEVE filters, support for SyncML 1.0, LDAP-based user management with single sign-on authentication, and LDAP contact databases. GROUP-E also provides ActiveSync for synchronization.
mujMail is a powerful and graphically atractive email client for mobile devices. Its operations are multithreaded, so you can send mail, retrieve mail from multiple mailboxes, and change settings simultaneously. It uses RMS to store mail messages persistently on the device, so don't have to connect to a server to read old mail. It has the unique ability to redownload a damaged message or body part and repair it.