Courier
Double Precision, Inc.
Free
The Courier mail transfer agent (MTA) serves as a comprehensive mail and groupware server that utilizes widely recognized protocols, including ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Within a unified framework, Courier delivers a range of services, such as ESMTP, IMAP, POP3, webmail, and mailing list functionalities, allowing users to easily enable or disable specific components as needed. Recently, the Courier mail server has introduced fundamental web-based calendaring and scheduling features within its webmail module, with plans for more sophisticated groupware calendaring capabilities to come shortly. Notably, the source code for the Courier mail server is designed to compile on most POSIX-compliant operating systems that utilize Linux or BSD-derived kernels, and it can also be successfully compiled on Solaris and AIX systems, provided users utilize the appropriate freeware add-on tools from Sun or IBM. The development of the Courier mail server is rooted in a combination of several interrelated projects that converged into its current form, and it also incorporates SMTP extensions specifically aimed at enhancing mailing list management functionality. In this way, Courier not only serves as a versatile mail server but also as a collaborative tool for users seeking effective communication solutions.