Microsoft on-premises server product that runs Office Online.
" ... IT IS A MICROSOFT PROBLEM WHICH MICROSOFT MUST SOLVE."
Actually, it isn't. I will explain.
You realize, of course, that the email addresses of just about every adult who has sent or received an email are floating around on the internet, where 'entrepreneurs' scoop them up, categorize them in many different ways, and then sell them to spammers all over the internet.
These spammers are very sophisticated, and they hire psychologists, engineers, marketing specialists. and other professionals to help them. One of the things they have to do is to come up with a spam campaign that their unfortunate victims are likely to fall for. Well, everyone wants virus protection, and McAfee and Norton are two of the best known names in that business throughout the world, so the combination makes for an excellent spam campaign.
There are many spammers all over the world who have the same idea, and some of them clearly have your email address too. So you - and me and millions of other people - are getting the same campaigns from many different spammers.
Microsoft didn't supply our addresses to these spammers, and nobody can stop someone from sending email to you, just as nobody can stop someone from coming up to you in public and saying 'hi'. Email addresses get into the public domain in so many ways: data breaches, intercepted in transit, stolen by malware, and increasingly they are being phished. That means people are unwittingly giving out their email addresses (and passwords) to scammers.
It's extremely difficult to stop a spammer. It takes the combined efforts of large technology corporations (like Microsoft) and cooperating governments to root them out, and the victories are few far between.
The best that we can do is to keep our spam filters updated.