Unwanted email can come from many sources.
Any amount of unwanted email can be difficult and time consuming to deal with. Often the most expeditious option is just to delete the unwanted messages from your inbox. However, it is common courtesy to reply to a sender who has obviously misaddressed a personal message. Preventing receipt of unsolicited mail and trying to take action against those sending it can be difficult to impossible. These may be applied to avoid getting unwanted email, but it can be difficult and will probably have limited success because it is very difficult to anticipate ways to identify an unwanted message and to be confident that you won't be discarding messages you do want.