Write an article based on this "Be selective about who you send letters to. Begin with the date you're leaving and a short explanation. Use the second paragraph to establish what the person meant to you. Say what you enjoyed about working there. Keep the letter positive. End with your contact information and a positive closing."
For the most part, you should only send out emails to people you know directly. Send emails to people you were friends with, co-workers you got along with but didn't know as well, people under you, and your manager. The exception to this rule is if you've been at the head of the company for more than 3 years. In that case, it's fine to send out an email to everyone in the company. The opening paragraph should establish the purpose of the letter, the fact that you're leaving. Include the date of your last day and the reason you're leaving, if it's appropriate. For instance, saying you were fired is probably not the best thing to include; however, if you're taking a position at a new company, you can include that information in letters to your friends. For example, you might write, "Just dropping a note to let you know that Friday, January 10 will be my last day at Rogers Incorporated. While I'm sad to be leaving, I know great opportunities are ahead." While a form letter is appropriate sometimes, such as when you're writing to the whole company, in general, you should personalize each letter to the person. Tell them how much you enjoyed working with them and what you appreciate about your professional relationship with them.  For instance, you could say, "I've so enjoyed working together with you during my time here. You've got a great mind, and I love how you are always able to settle disputes. I hope we can stay in touch in the future." For a more generic letter, you might write, "I'm so proud of the work we've done together at this company. You all are hard workers, as well as being creative and team-driven. Let's keep in touch going forward." This option works especially well in a less personal letter. It's a positive way to connect with the people who are still there, and it helps you end on a good note. For example, you could say, "I loved working at Rogers Incorporated. The relaxed atmosphere created the perfect environment for creativity to flourish. Everyone is so positive, and I'll miss that as I move on." A goodbye letter isn't the place to complain or air grievances. You definitely don't want to burn bridges that you may need later! Instead, stay positive and keep it civil. That way, you can still network with the people you worked with later. You never know when you'll need that connection. Your personal (professional) email is enough for most people. However, if you'd like to have the occasional lunch with someone, you might include your phone number or even home address. For a closing, you might write, "I wish you the best of luck moving forward, and I hope to hear from you soon!"