Player not exist but they can send me mail in game?

nurul23495

Hi. I'm Cross Yuki from server US83.
When I start playing this game, lots of player send me mails in game. When I want to reply it always "Input Player Name" when his/her name already have been put as the receiver. When I search their names in friend's section, it says "Friend not found"
I've been playing for months in other servers but this is the first time this happen to me