Postfix+dovecot+thunderbird offers a pretty good mail service.
Not to mention the K9Mail client on Android too. And roundcube is good enough if you have no access to the Laptop/Mobile which you always use.
It works fine for me for my company mails. Planning to switch my personal mail too. The only issue is that I have so many mailing list subscriptions and it needs time to switch over.
And I can sell my Apps account with 100 users, so that I can get enough money to run a VPS for atleast a few months