Fully-featured mail server which handles both transport and storage, and allows for easy extensibility using MailServlets (for example: send mails as fax or voice, filter mailets, translator, mailing list, newspaper via mail). [Open Source, BSD-like]

Newsletter software capable of publishing e-mail newsletter and maintaining the subscribers. This newsletter software written in Java, provides statistics and analysis for the published newsletters. [Commercial]

A full-featured SMTP/POP3/IMAP4 server with pluggable mail filters and agents for application processing. [Shareware]

Java mail server. Uses a JDBC database (free database InstantDB is provided) to store messages. [Open Source, GPL]

Java 1.5 certified email application server. [Commercial]

Very simple smtp pop3 java email server implementation with source. [Open Source, GPL]

A modular SMTP daemon (mail server) written in Java. [Open source, GPL]

A SMTP/POP3 server running under Java 2 Runtime Environment. Includes a list of features, original code base, and how-to configure it.

A very simple example of a POP3 server in java. [Open source]

A SMTP and POP3 email server. [Freeware, open source]