What is a good outlook replacement?

I have been using many email client by now. As a matter of fact, there are many email clients in the market with their merits and demerits. As per my suggestion, i would never ask you to buy an email client when you can get the best ones for free. As the best alternative for outlook, Thunderbird should work like a charm. One can even download add-on from its site and modify the email client making it more user friendly and personalized. Few more email clients that i can recommend are:

1. Claws Mail

2. Spicebird

3. Zimbra

4. Sylpheed

I would still recommend and stress Thunderbird before Outlook or any other email clients. There are huge set of features in thunderbird itself that it can make work flow easy and reliable. Features like:

1. POP and IMAP accounts can be created for practically unlimited email addresses

2. Account setup is fairly easy with the account wizard

3. Powerful and simple-to-use search tool

4. Awesome filtering techniques including tagging of emails

5. Saved searches are also included

6. Multiple viewing options, including vertical columns, two-row column, three-row column

7. Highly customizable and flexible

8. Message threading and conversation views possible

9. Advance address book adding with contact integration

10. Reminders for dates, tasks, to-do services, meetings and attachments

11. Tabbed message viewing makes it easy

12. Message archiving now possible

13. Easy adding personalized email addresses

14. Built-in junk filtering and virus protection

15. A migration assistant to help one move their accounts from other email clients like "Outlook", etc.

16. Open source add-on infrastructure for customizing as per user needs