adding patch from kernel-error.de for SPF, DMARC and DKIM graphs

Hi David, 

i search for dkim graphs for opengraph and found this german blog post. https://www.kernel-error.de/postfix/mailgraph-aufgebohrt

Maybe you are interested to merge this in your code for future releases. i havn't tested it but in the next days i will do it on my mailserver. 

Regards