Farewell cards to employees or colleagues, who are among the most common recipients, might include poetic thoughts such as, "A new job is like a blank book and you are the author," or else just a simple "Good luck!" For close friends, a more personal message or quote might be appropriate, such as, "Don't cry because you are leaving. Smile because you were there."
Sometimes, a person, particularly in the workplace, will want to send a farewell message to a number of people at once. In this instance, mass emails are generally more convenient than cards. Messages of this sort might be either heartfelt and optimistic or else frank about one's negative feelings, perhaps towards their employer.