libdkim++ is a lightweight and portable DKIM (RFC6376) library for *NIX, supporting both signing and DMARC/ARC/SDID verification, sponsored and used by Halon Security. libdkim++ has extensive unit test coverage and aims to fully comply with the current RFC.
I experience issues trying to rebuild libdkimpp against openssl-1.1.0e (which is landed to Fedora devel). Seems not compatible with this branch, please see 18270389 build log for more details.