I want to test JavaMail locally, so I need a mail server. Are there any free mail servers I can use?
There is also very simple in use GreenMail which was designed as a mail server for automatic unit (self-integration?) tests.
From projects web page (maybe there are some others tools with that functionality nowadays):
GreenMail is an open source, intuitive and easy-to-use test suite of email servers for testing purposes. Supports SMTP, POP3, IMAP with SSL socket support. GreenMail also provides a JBoss GreenMail Service.
GreenMail is the fist and only library that offers a test framework for both receiving and retrieving emails from Java.