Large-scale active measurements of DNS entries related to e-mail system security

Since its early beginnings, e-mail has been one of the most successful Internet services as it was the first to offer global, asynchronous and almost instant message delivery. However, at the same time e-mail has not been designed with strong security considerations in mind, leading to various problems related to unsolicited messages. In order to mitigate this situation, since the mid 2000s, domain-based message authentication mechanisms have been standardized and deployed which mostly rely on their specific entries in the DNS. In our present paper, we provide the results our measurements of such entries for the SPF, ADSP and DMARC technologies for the Top 1 Million Alexa sites over a period of four months in 2014. While we have found many expected types of entries, we were also surprised at the non-negligible number of either too lax or too strict policy configurations, which we comment upon in detail, along with analyzing interesting correlations in cross-technology configurations. After providing valuable insights into the current status and the trends in SPF, ADSP and DMARC, we conclude the present paper with an outlook on our future work.