The current OpenWRT version (220.127.116.11) has Exim 4.96 compiled without Sender Policy Framework (SPF) support.
The library ( https://www.libspf2.org/ ) on which it depends does not seem to be part of OpenWRT.
I'm not sure what the thing to do is. Is it bad form to email the account of the OpenWRT package maintainer as entered in the Makefile?
Or is it better to "log" it somewhere?