This feature seems to be required by so many people that I'm surprised that few desktop apps actually provide it. Thunderbird does, with its Lightning (and Goog

This feature seems to be required by so many people that I'm surprised that few desktop apps actually provide it. Thunderbird does, with its Lightning (and Google calendar) extension. The still-not-ready-for-widespread-use Chandler (http://chandlerproject.org/ http://chandlerproject.org/) project was another attempt at this.