Reader Dave Haas doesn’t care for Mail’s Out-landish behavior. He writes:
When sending a message in Mail with a very large attachment—as Mail chugs along sending out the message—oftentimes a new mailbox appears named “Outbox.” Typically this new mailbox will hang around for a while long after the message is sent and then eventually, mysteriously disappear. Is there anyway to get this mailbox to remain permanently? And part two of the question: Is there any way to stop a message from being sent once I’ve clicked on the Send button? It seems that the “Out” box might facilitate that.
Unlike with Microsoft Entourage, which always displays the Outbox, Mail causes the Outbox to appear only under certain circumstances. Specifically, you’ll see it if you’re offline, have composed a message, and instructed Mail to send that message. Because you’re offline, Mail can’t send your message and so it shoves it into the now-visible Outbox. When you’re back online, anything in the Outbox is sent and then Outbox, having done its job, disappears from sight. The Outbox will also appear if a message isn’t delivered by your Mac—either because the connection has been broken or you’ve decided to not complete the transmission and have clicked the Stop icon in the Activity Viewer window.
I suppose you could force the Outbox to be always visible by composing a message in a particular account, taking that account offline, sending the message (and, thus, sending it to the Outbox), and then never taking that account online again, but I’m not sure why you’d want to.
I hinted at the solution to your second question. If you have a message that’s halfway out the door and you’d like to stop it, choose Window -> Activity Viewer (Command-0 [zero]), and click the Stop button. It will be placed in the Outbox.