Spam Emails Attributed to Microsoft

For about the past six months, I have received more than 100 spam messages that Spamcop attributes to Microsoft IP addresses and reports to abuse@messaging.microsoft.com, junk@office365.microsoft.com and spamloop@frontbridge.com

The spam sender adds a template to an old, legitimate email message which includes two links to images and two links that redirect to sites such as http://emailtrust.xyz, https://impalos.com, https://www.seedleafitem.com and https://yuzuapples.com.

When I analyze the headers at https://toolbox.googleapps.com/apps/messageheader/analyzeheader, they often show a delay of hundreds of days from a Microsoft IP to my Verizon.net/AOL/Yahoo server.

So I'm asking is Microsoft at fault? How are the spammers able to do this? Can it be prevented?