GreenMail is a suite of email servers for testing purposes and sandbox development. It supports SMTP, POP3, and IMAP (including SSL) and can be embedded into any Java application or unit test. The GreenMail Service (SAR) extension runs as a JBoss embedded developer mail server sandbox, manageable via JMX.
Designed as a Perl framework to support many different types of POP and email servers, Mobile POP Relay is useful for mobile users. Once a user successfully authenticates against a POP server, relaying is allowed through the server for a specified time period. It supports Ipop3d, Qpopper, and Vpopd with Sendmail or Exim.