This is the key:
Received-SPF: fail (google.com: domain of newsletter@bulten.mywebpage.com does not designate 213.xxx.77.226 as permitted sender)
There should be text record in the DNS of bulten.mywebpage.com in spf format that points to the mail server sending out the mail, something like this:
v=spf1 mx mx:mailserverdomain.com