There is no fail-safe way to ensure people on the list are who they say they are and have suffered the loss they describe. Occasionally, a list member has been found to be perpetuating a hoax. The best way to handle such morons is to pity them, forget them, and go on with your griefwork. That said, these mailing lists are typically peopled by very compassionate and non-judgemental individuals who are just as vulnerable and suffering just as much as you are. There are a couple of survivor-oriented lists for those who have experienced suicide loss.
Most websites described here have one or more message boards.
Jump to Resources for a list of websites. There are probably a few hundred newsgroups devoted to grief and bereavement issues. Please check with your local internet access provider or DejaNews for further information on finding newsgroups. I will post survivor-specific newsgroups here as I find them. Many survivor lists, depending on type of loss.