According to Freud, an envelope is a symbol of female sexuality and putting a letter into an envelope represents sexual intercourse.
If the envelope is left unopened, this may represent virginity or sexual repression. Leaving a letter unopened in an envelope may also suggest that you are not taking advantage of an opportunity in real life. In dreamland, as in real life, envelopes are symbols of mystery and we can never be really sure of what they contain until we open them.
If you are awaiting news about something or someone and dream of holding an envelope in your hand, your dream is probably just reflecting your anticipation.
If you open the letter and discovered either positive or negative news, don’t read too much into it; your unconscious was probably just mirroring your fears or fulfilling your deepest wishes. In other words, your dream may come true in waking life but it also may not.
If you had a dream in which you received an envelope and recognized the handwriting of an old friend, this may reflect your desire to see them again.
If you are struggling financially and dreamed of shoving envelopes into the dustbin, this message from your unconscious is a warning that if you continue to ignore your financial situation, your unconscious will continue to send you such dreams until you deal with the problem in real life.... The Element Encyclopedia