Re: 800lb Gorilla over there sitting beside the Elephant...
What on earth is in Outlook that any competently engineered mail client is lacking? I shifted from a happy user of Thunderbird accessing an IMAP server to having to use Outlook+exchange, and have daily fights with the thing that has come close to me flinging my MacBook through the nearest window. Outlook is a *ckin UI disaster, and it's interaction with calendars and contacts appalling. That there is nothing better out there for corporate environments is a disgrace. It will never improve over what it is now without some competition.