A recent spam campaign seen by SophosLabs shows how the spam has changed (probably deliberately) to get around blocklisting. Blocklists have a relatively good success rate at blocking spam (~90%) however they do not work for all types of spam. The original messages in this campaign had a fully formed URI however as you can see from the above image in subsequent messages the last dot has been replaced by two spaces. Fooling either a human or a computer is a relatively easy task but fooling both is difficult.”]
Source: https://nakedsecurity.sophos.com/2009/02/07/spammers-must-fool-humans-and-computers/