A brief reminder of the SMTP protocol

Figure 1 - Example of spam advertising for luxury products

Figure 2 - Example of software spam

Figure 3 - Example of gambling advertising spam

Figure 4 - Example of game spam

Figure 5 - Example of phishing spam  – winner of a loteie having to call to give bank details

Figure 6 - Example of phishing spam  – request to enter login information following fraudulent use of your account

Figure 7 - Example of hoax spam

Figure 8 - Example of scam spam

Figure 9 - Example of spam carrying malware

Figure 10 - Breakdown of spam by content over the 1er half-year 2008

Figure 11 - Email exchange architecture components

Figure 12 - Bypassing keyword filtering by modifying/adding characters

Figure 13 - Bypassing keyword filtering by encapsulating text in an image

Figure 14 - Bayesian filtering bypass example

Figure 15 - Example of foreign-language spam

Figure 16 - Example of how to circumvent character recognition techniques in images [24]

Figure 17 - Example of how to bypass URL filtering

Figure 18 - Example of a CAPTCHA – rewriting the word read

Figure 19 - Example of a CAPTCHA – on an image, circle the object corresponding to the word read

Figure 20 - Example of a CAPTCHA – from a list, choose a word that best describes the image

Figure 21 - Example of how a Turing test-based anti-spam tool works

Figure 22 - How greylisting works with a legitimate mail server

Figure 23 - How greylisting works with a spamming mail server