Sent messages will appear in either the Outbox or the Sent messages folder. As long as the recipient(s) have not yet read the message, it will stay in the Outbox. As soon as someone reads the message it will be archived to the Sent messages folder. If the administrator allows it, you can edit messages after sending them as long as they are in the Outbox and the recipients have not yet read them.
It does not say anything about opening the inbox, but specifically mentions the message.
--Andy