We are aware of an issue where some of the players on the NA servers are unable to see the contents of their mailbox (despite there being a notification about new mail).
We have identified the cause for this issue and we will continue working on resolving this.
We will update this notification as soon as new information is available.
We do apologize for the inconvenience caused and thank you for your patience!
[UPDATE - SEPTEMBER 2022]
This issue was resolved after maintenance.
Thank you for your patience.