Junk or not Junk

So a message from 

Benilton Carvalho <bcarvalh at jhsph.edu> (sent by
r-help-bounces at r-project.org)

 arrives and goes in the Junk Mail even tho I have set @r-project.org to not
be junk

Why does this go in Junk mail if @r-project.org is defined as not junk?

If we knew what we were doing, it would not be called research.
Einstein