If you are using yahoo mail, like me, then you missed for a long time IMAP access for your inbox. They provide just POP3 access and I don't want that. I would like to have/access the messages also via web interface and also to have them on my computer for offline access. So, the solution is Zimbra Desktop and you can use it on Windows, Linux or Mac.
"Zimbra software is open source, meaning we make both the software code and the application itself available to anyone at no charge. Also, Zimbra Desktop is a full version; there are no missing features or catches"
For a complete list of features see this link: http://www.zimbra.com/products/desktop_features.html
If you have any issue with it you can find the answer on their wiki.
Here is just a screenshot: