Depends. Ability to read the sent message has nothing to do with the delivery of it.
If it's still in your OUTBOX, then you can still read it. That means the email is stuck on your side of the server. However, if it's not in your OUTBOX, then most likely it has already left your server, and it's somewhere out there, floating along to get to the recipient.
If it's already gone, and if you the sender have saved a copy in the SENT or SAVED folder (some system admin automatically setup this option for you), then yes, you can read a 'copy' of the file. If this is not setup, then no. You won't be able to read it because you don't have a copy saved on your side. It doesn't matter if the email is delivered or not.
The reciever will obviously not be able to read it until it's delivered.