In Korean tradition, dreaming of a letter is read as mixed. It is most often tied to 전반, 애정.
A letter is awaited news — good contents, glad news; an unreadable letter, no answer yet. A parcel arriving, something unexpected coming.
Tradition reads the symbol as an omen; psychology reads the same dream as a mirror of your present state. Describe your dream and both readings appear together. Interpret your dream