Version:           unknown (using KDE 3.1.0)
Compiler:          gcc version 3.2.2 (Mandrake Linux 9.1 3.2.2-3mdk)
OS:          Linux (i686) release 2.4.22-10mdk

Tabbed email changes the way you use your email client by allowing you to open 
email views (folders, messages, composers) in background tabs and then work 
with each of them in turn.  Tabbed email makes it much easier to keep track 
of several email related tasks at once by letting you manage them in a single 
pane.  No longer will you have to jump around from message to message to 
collect information or look for the composer screen in your taskbar.  Each 
view aligns side-by-side, allowing you the most efficient experience in email 
messaging.

There is no reason that each and every screen in the email, 
except for the folder list, can be part of the tab set.  The way it works is 
that the list of message for a folder (say the Inbox) would be the first tab 
to appear, and when you double click on a message it opens that message in a 
new tab (or perhaps right click "open in new tab").  Composing a message 
could also use a new tab.  This way, you can have the message you are 
replying to in an adjacent tab to the message you are composing, so you can 
flip back and forth during your response.  Additionally, you might want to 
queue up a bunch of messages that need attention, so you open them all in 
tabs and handle them in turn (how many times have you marked messages as 
important hoping that it will remind you to reply?...now you can just open 
them all in tabs and not close them until you do!).

Below is a screenshot of concept art demonstrating this feature.

http://www.mojavelinux.com/cooker/incoming/tabbed-kmail-concept.png

While the implementation may appear to be straight forward, there are a number 
of configuration settings that will be introduced by this change.  The list 
includes:

* compose messages in new tab (vs window)
* read messages in new tab (perhaps a context menu option to open in new 
window or new tab)
* open mailbox in new tab (perhaps in context menu, so as not to replace 
current "folder" tab)

As I have shown in the screenshot, I believe that each "type" of tab should 
have an icon and a prefix, using the spot of the favicon from Konqueror.  
Prefixes would include:

"Folder:" - for a folder list of message
"Message:" - for viewing the contents of a message
"Compose:" - for composing/replying to a message
"Attachment:" - for viewing an attachment from one of the messages