We need anti-spoofing techniques in order to be able to recognize TEAs(Trustworthy Email Addresses), which becomes trustworthy thanks to the use of a TSF(trust/risk based security framework). Obviously, ourtechniques differ regarding their security strength or level of confidence in recognition. However, there is no exact way to say that one technique is weaker than another one. For example, it is not straight forward to choose which of the following offers the higher level of confidence: a valid signature with a very short asymmetric key, which has been used for years, or the ability to show that the sender is able to receive emails sent to a specific email address