I'm open to correction here, but I think it is an attempt to look as though the sender takes part in a scheme such as Sender Policy Framework (SPF), which is intended to provide for proper authentication of the sender of an email. Not being a participant in SPF, I have no emails to compare this one to, unfortunately.
SPF has other elements than this "Authentic Sender" anyway, without which it doesn't work as a system: it involves amended DNS entries, as I understand it.
So taking your first example, what we have is a spammer inserting "clues" designed to fool an unsophisticated mail agent or recipient into thinking the message has some kind of spurious validity. All too common, unfortunately.
If you invest in some client anti-spam software that uses "Bayesian" methods, you can train it to recognise and bin things like this. One example (for Outlook users) is Outclass/POPFile.