For testing you can use Mercury. Just start it in the Control Panel. Predefined Accounts are Admin@localhost and postmaster@localhost. Sending Mails to them should work without problem, getting Mails will not work as they do not have a password. To change the passwords, click the Admin-Button in Control Panel for Mercury and select in the Menu Configuration -> Manage local Users. You can now either add a new user (the E-Mail Address will be username@localhost) or change an existing user (and enter a new password for this user). Then you will be able to retrieve the mails for this user by your preferred Mailprogram. You can either use IMAP or POP3, Mercury supports both, Server is localhost, username the username you wish to download the mails from (without @localhost).