Most non-profits I know are skittish about direct mail fundraising, because it requires an initial investment of time and money. Picking up the phone to call a donor takes courage, but it doesn't cost money. Sending out an e-mail is easy and free.
If you're in a very large charity, your direct mail fundraising is most likely outsourced. If your charity is small, you likely do it all by hand. This is a guide for anyone somewhere in the middle.