I've noticed this is the behavior used by many e-mail clients: when I double-click a message in the inbox, it gets opened in a new window. Similarly, when I compose a new message, the composer comes up in a new window. I find my system too cluttered when a new window opens for each message. I'd really like a feature wherein the message (to read or to compose) opens in the same window as the inbox list, replacing the inbox list (or whatever list is open), so that I really only ever see one window. Then, when I'm done reading or writing, I either close or send that message, and return to the previous view. Eudora follows this model and I really like it; it seems very clean. It would be cool to have a checkbox in preferences allow this behavior.
this is RFE.
*** Bug 157048 has been marked as a duplicate of this bug. ***