Here’s a good site on interface design and one about Human Cognitive Abilities from Berkeley:
Simplified design has always been a good practice. Basically, the more your application can do in one key or button press the better. Of course there are always limitations to this whole thing based on requirements for data collection, et.al.
As far as email goes, I’m kinda partial to Thunderbird. Its recipient boxes are quite intuitive in that you don’t have to type, just click and drag and click again. For more recipients, move down one box and repeat. However, this requires entries in your address book. That too is rather nice in that Thunderbird will automagically add any newly typed address. Then, it’s subject (if desired) and body combined with send. Granted, it’s not perfect, but it’s leaning in the right direction.
What is truly needed to really bring this all to a simple interface design is Matrix-like connections. Then we are all networked and we don’t need to use these software interfaces. Or, the Star Trek: Next Generation computer. (“Computer.” “Yes, captain?” “Send my mother an email.”)
There is the “new” technique of user acceptance. That’s where you dummy up an interface and populate dummy data then give it to a set of users to see how they like it. Then, with ears open and mouth shut, you listen to them and take copious amounts of notes. Then go back to your computer and try again. Once you have another “prototype” you start back at giving it to the set of users then repeat until the users say, “I like it!”
This all depends on what the other departments (security, business, etc.) all say. But however it’s presented, user acceptance should always include interface design. It’s the user that’s going to be using the application more than the developer probably will and that’s the person who should drive your interface design, the user.
All the design courses/classes/seminars/websites in the world don’t mean a thing unless the user, the one using the application, feels comfortable and possibly (hopefully) productive. Just like using a graphics program for graphics design, good UI design doesn’t come easy, it takes practice.