Graph seems wrong
The graph shows disruption at 23:55ish
Even if it means 23:55 BST, it's still about 10 minutes later than Google reported (and I noticed)
Strange
9 publicly visible posts • joined 13 Jun 2012
this is where the DKIM comes in - DKIM signatures remain valid so long as the message is forwarded verbatim
DMARC allows one of SPF and DKIM to fail without the message being rejected - it can be seen as combining the strengths of the two systems and avoiding the weaknesses