Provided by Yahoo!

Zimbra Desktop is free. 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.

• A Better Inbox
  Unlimited email storage is great but searching through thousands of emails is a hassle. Our Conversation Views and Message Tags automatically highlight important emails in all your email accounts so you can find anything in a hurry. Advanced Search makes finding important pictures, documents or messages from people you care about a snap.
• All Your Email Accounts in One Place
  Zimbra Mail. Yahoo! Mail. Gmail. AOL. They all work automatically in Yahoo! Zimbra Desktop; even Outlook or any other work or personal email account using POP or IMAP is easy to set up. The best part—you can read them offline without an internet connection when you are in "airplane" mode.
• Looking to Replace Outlook?
  Yahoo! Zimbra Desktop combines the best aspects of existing email clients (also known as POP or IMAP email clients) with modern webmail applications to make a totally new and improved experience.

Nowhere else will you find an application with full email, contact, calendar, document management and offline access features for free!