JMultiSend
A simple and fast cross-platform solution to send mass emails.
...It is possible also to manage mailing lists subscribtions simply by emails, to send personalized messages with username and to schedule delays up to 24h (86400 secs); all this also from command-line. Since it is developed in Java it is a cross-platform application and does not need installation but needs only the Java Virtual Machine (version 6 or higher) that, in the case, is very easy to download and install.