Update 'src/mailsrv/docs/Resources.md'

src/mailsrv/docs/Resources.md

@@ -7,6 +7,9 @@
   - says to use `@` for subdomain, but Dyn only accepts `*` as wildcard
 - https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy
 - https://www.linuxbabe.com/mail-server/create-dmarc-record
+- https://www.rackaid.com/blog/email-dns-records/
+- https://www.skelleton.net/2015/03/21/how-to-eliminate-spam-and-protect-your-name-with-dmarc/
+- https://seanthegeek.net/459/demystifying-dmarc/
 
 ## Best Practices