Blacklist prevention

A blacklist is a basic access control mechanism that allows through all elements like email, address, users and domain names except those explicitly mentioned. Blacklist can be applied at various points in security architecture, such as a host, web proxy, DNS server, email server, firewall, and directory server. A good number of companies have their emails blacklisted in the firewall. To avoid those, keep the computers updated and block the outgoing traffic on port 25.