What is your favorite PHP webmail?

I use SquirrelMail because it is shipped with cPanel and it works fine,
but I just don't like it at all. I like Uebimiau, but then there are its
stability and security issues, and it seems development has been
discontinued.

I was wondering what your favorite web mail is...
I'm looking for an AJAX + PHP webmail if possible (easier than Zimbra).
Thank you,

--
Charles.

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