In a UPN, how many characters can be entered before the $"$@$"$ symbol, and how many characters can be entered after the $"$@$"$ symbol?

answer

$48$ before and $64$ after the $"$@$"$ symbol

$48$ before and $48$ after the $"$@$"$ symbol

$64$ before and $64$ after the $"$@$"$ symbol

$64$ before and $48$ after the $"$@$"$ symbol