First things first – turn outlooks offline feature on. This will stop outlook from attempting to send and receive emails.
Next move the offending 2 messages from the outbox to a temporary folder.
You can now hit send and recieve and have all you new email flow in.
Next move one of the problematic emails to the outbox and try to do a send and recieve.
If it works move the other one as well and do the same thing.
If not delete the ones that are giving you an issue.
Turn Outlook back to Online.