According to a study conducted by email marketing experts Lyris, there is “an increasing reliance on the Sender Policy Framework (SPF) authentication method” to determine the legitimacy of inbound mail.
SPF is an open standard method to prevent sender address forgery. The solution to combat fake email works via a delivery policy specified in the domain’s DNS zone records. The receiving server can check whether a message has complied with the domain’s stated policy before conducting further checks.
The study, which monitored almost half a million messages, shows that permission-based email is delivered roughly 75 percent of the time to major ISP inboxes. Further examination showed a decrease in image spam and an increase in spam using PDF, PowerPoint or Excel files.