The next page shows you the mailmaps you are about to create, and asks you to double check that they are correct before finally adding them to the system. You will want to check that the aliases are what you intend, and that the destination addresses are entered correctly before you click "next" to confirm the changes and add it to the system. One of the most common causes for a failure in email forwarding is a misspelled destination address, so make sure they are all spelled correctly before you commit them.