To dream of receiving mail represents news, information, or insight that you're supposed to have. Information that is helpful or purposeful. A signal of some kind that you have been expecting from someone. Personal or exclusive matters.
To dream of sending someone mail represents news, information, or opportunities that you are revealing to someone else. You may believe that someone needs to know something. It may also reflect personal or private matters exclusively between you and someone else. Negatively, it may reflect an attempt to embarrass someone in a very personal way.
To dream of waiting for mail represents a news or information that you are expecting updates about. You may need to know something before you can proceed with a situation. Expectations you have with a person you are interested in dating.
To dream of mail that is lost may represent feelings about having lost out on opportunities that you were expecting. Delays or setbacks may have gotten in the way of someone giving you important or helpful information.
Negatively, mail in a dream may reflect expectations from people to communicate with you that are naive or imbalanced. A sign that you may need to initiate contact, communicate, or send a signal to someone first in order to get the response you are looking for.