Cyrus is an advance IMAP daemon widely used in small to large scale organizations. It is a full fledge IMAP system and offers some greater advantages over other freely available IMAP alternatives. It is designed to handle massive flow of emails effectively, and it runs on “Sealed†servers where normal users are not permitted to login. Alongside IMAP, it also support POP protocol for email retrieval and provides ability to setup and mange quotas on emails/accounts. Read more at LinuxPitstop
