Atmail is a fully-featured email server and Webmail client, allowing users to send and receive email via a Web browser or mobile device. It has full support for IMAP mailboxes, and an optional email-server mode that uses EXIM as the MTA. Features include a scheduler, MySQL backend support, spell-check, address book, calendar user preferences, multiple accounts, SpamAssassin support, migration scripts from other mail servers, a customizable interface, an attractive AJAX interface, an optional group sharing Calendar/Addressbook, and an Outlook plugin to sync Contacts/Tasks/Calendar data between a Desktop, Mobile, and Webmail client or other email users.
GroupOffice is a groupware suite that takes your office online, implementing online collaboration and CRM. It allows you to share projects, calendars, files and email online with co-workers and clients. It is easy to use and fully customizable. It also features synchronization with PDAs and Outlook.
Forwards is a Horde module for setting user e-mail forwards via the .forward mechanism supported by several popular mailers. Forwards provides fairly complete support for setting .forward style forwards on Sendmail, Courier, or Qmail based systems via an FTP transport. It also has drivers for Mdaemon, Exim SQL, Exim LDAP, Custom SQL, and SOAP based systems.
MIMP is a version of the popular webmail client IMP intended for mobile phones and PDAs. Basic webmail functionality is implemented, including mailbox viewing and paging, viewing messages, deleting, replying, forwarding, and composing new messages. It utilizes the Horde Application Framework.
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.