At first glance, I thought it was missing as well, but if you look closely, you can see the letter further down in the list (as it was supposedly sent on Day 91, 14:29). If this is not correct, do let me know, since I'm not sure if it's supposed to be a message that has to be resent and wasn't doing it properly.
In any case, I've added a toggle filter to hide all read messages for the next release. Hopefully this will help with any visibility issues with the mail.