I hate to admit this, but the mobile space, iOS and Android, is really where the attention is being paid where email apps are concerned. The desktop space has become dominated by free webmail monoliths like Gmail and Yahoo. The corporate/business space is dominated by Outlook and... Gmail, yup. Thunderbird was the only strong, independent email app I ever liked since Eudora become stupid years ago. But these days that entire desktop email space has been a vast wasteland. And yet, on mobile devices there is still so much development going on. Look at Outlook mobile (once an independent app called Accompli). The app is great, integrates with Gmail perfectly, and makes reading my work email on my mobile device almost a better experience than on my desktop.