Log Message:
Add RequiredFrom option

If RequiredFrom is set, opendmarc will reject messages that lack
a From header from which a valid domain can be extracted. This
is a subset of the full RFC5322 requirements enforced by the
RequiredHeaders option.

While non RFC5322-compliant messages are too common to make
RequiredHeaders always usable, the check on the From header
remains especially valuable. It makes sure forged domain messages
cannot evade the filter by just omitting the From header and relying
on the MTA to fill it by a copy from the enveloppe header.

Submitted upstream as
https://github.com/trusteddomainproject/OpenDMARC/pull/147