Sometimes it just takes a little while so this isn't necessarily unusual.

Just to confirm though, when you said you deleted all open mails, was this including all previous ones from Square Enix? Although we can receive more regular mails from other players, there's a limit of only 20 emails from Square Enix so if you have any of those you'll need to get below 20 (there's a counter at the bottom to show how many of those specifically you have). Once you're below 20 in most cases just pressing redeliver will work/arrive within a few minutes, but if not recommend just give them a few more hours before panicing.