How to verify an email address change to a new mailbox

How to verify an email address change to a new mailbox

I am attempting to change the primary address of my admin email account.  I was successful at updating my address under the profile menu from xxx@mydomain.com to yyy@mydomain.com and I can login using the new address as login credentials, but the change has not propagated through to my mailbox.  The mailbox still shows as xxx@mydomain.com after logging in to yyy@mydomain.com

After reading through user guides, it sounds like i may need to cosnfirm this change by replying to an email sent to the new mailbox, but in order to do so I need to access the new mailbox which has not yet been created. 

What is the best way to extend a new profile email address to a mailbox without being able to access the new mailbox?

Thank you