Friend doesn't receive mail.
1. Did he have any special characters in his name? “Öwl”, for example, is different from “Owl”. Users can use special characters to get names that they want if the regular spelling is taken. Though, this can cause problems as not every user has a complete list of alt commands on hand and must wait for the other user to contact them to get the name verbatim.
2. Are you sure this ‘friend’ of yours isn’t BSing? I’ve have heard many cases on other pixel games/sites where they have lied in attempt for a user to send more.
Have him check his mail queue. 10 is the max that will show. To get more he needs to delete old mail until the new mail starts arriving.