Bug#528344: exim4-daemon-heavy: Please add SPF support

[Simon Josefsson]

Hi!  I read the exim4 manual on SPF [1] and tried the example on my
Debian buster server (even tried 4.94 from buster-backports) but
discovered that exim4 wasn't built with libspf2 support, and stumbled
on this old bug report.

Is there today any reason exim4-daemon-heavy isn't built with libspf2
support?  Could this be revisited?

Thanks,
/Simon

[1] 
https://www.exim.org/exim-html-current/doc/html/spec_html/ch-dkim_spf_and_dmarc.html#SECSPF