Blacklist Check is a free online service which will check to see whether your email domain has been blacklisted for transmitting spam or malware. It searches through a comprehensive 147 lists, which means if there is trouble they should find it. A very useful resource and especially valuable if you notice email messages going missing in increasing numbers. One for the bookmark pot.
This test will check a mail server IP address against 147 DNS based email blacklists. (Commonly called Realtime blacklist, DNSBL or RBL). If your mail server has been blacklisted, some email you send may not be delivered. Email blacklists are a common way of reducing spam.