Blackmail suggests that there is a part of us that is aware of information that we hold. However, we have difficulty in sharing that information with others. We may also be called upon to account for past actions.
Psychological / emotional perspective: For many people privacy is a very emotive issue and to dream of blackmail suggests that someone has penetrated our defences, probably in an inappropriate way.
Material aspects: When there is conflict between two courses of action, to dream of blackmail suggests that we are being forced in some way to take an action which goes against our natural instincts.
If you dream of someone trying to blackmail you, it is a warning against indiscreet behavior with someone of the opposite sex.
If you were the blackmailer in your dream, you would be wise to avoid any type of gambling because you will be unlucky.