But, then, what would be the reason for the "outbox"...

Should I better have sent my former pm's by using the "sentbox" to be sure they have been sent more effectively? Will a pm I am sending by the "outbox" reach the addressee, or should the "sentbox" be utilized?
And why is it called "sentbox" (it's past tense of the verb send) instead of "sendbox"?
