How do I retrieve emails that were not sent while my iCloud storage was full?

My iCloud storage filled up and therefore stopped my email from receiving or sending emails. I ignored this as I thought did not need any emails, but I was sent an important email during this period of my email being disabled. I have upgraded my iCloud storage and it is no longer full. I am receiving emails again but I cannot retrieve the emails that were not sent during the time it was down. How do I retrieve these emails?