Email Blacklist:A list of Internet Protocol (IP) addresses or domains that are perceived to be sources of email spam (unsolicted commercial email).
Blacklist Monitoring:The use of a software application to automatically monitor blacklists for the inclusion of certain IP addresses. Monitoring blacklists is considered a preventative measure for legitimate bulk email senders, so that they can address any blacklisting issues proactively.
RBL:RBL stands for realtime blackhole list. An RBL is a list of Internet Protocol (IP) addresses whose owners are believed to be spam perpetrators/proliferators. RBLs typically list server IP addresses from companies and service providers whose customers are responsible for proven spam and from Internet Service Providers (ISPs) whose servers have been compromised/cracked for spam relay.
DNSBL:DNSBL stands for DNS Blacklist or DNS Blocklist. It is an RBL that can be queried via the Internet and DNSBLs are therefore used by companies to block spam from reaching their internal servers.
ORBS:ORBS stands for Open Relay Blocking System. It is a method of checking, in real-time, to see if an email message came via a proxy, or open relay server. If it did, then it is considered to be spam.
Open Relay Server : An Open Relay Server is an email server that allows a third party to relay e-mail messages, i.e., send and/or receive e-mail that is not for or from a local user. Note that Open Relay Servers don't always indicate spam. They could be relaying email from a remote user to the corporate server(s) for processing.
Proxy Server :A Proxy Server is a server that sits between your web browser (or client application), and the destination server. The proxy server then acts as an agent on behalf of your browser (or other application). In addition to many legitimate uses, spammers may use proxy servers to hide the true origin of their bulk email.