Because bitcoin.org's SPF record's failure mode is set to "softfail" rather than "fail" [1]. According to Wikipedia, "Typically, messages that return a SOFTFAIL

Because bitcoin.org's SPF record's failure mode is set to "softfail" rather than "fail" [1]. According to Wikipedia, "Typically, messages that return a SOFTFAIL are accepted but tagged". [1] http://mxtoolbox.com/SuperTool.aspx?action=mx%3abitcoin.org&run=toolpage http://mxtoolbox.com/SuperTool.aspx?action=mx%3abitcoin.org&...