Organizing and accessing contact information in Outlook.com
I added the *delete all emails except if the sender address contains* "@" rule days ago and I still get emails with no sender address. So it doesn't work. So why are you spamming all these replies here and patting yourself on the back if you didn't even test your own suggestion?
Clearly Outlook is a horrible email service if it allows millions of spam emails with no sender address to be sent to millions of people. Clearly Microsoft doesn't care if they don't even reply to any of these threads. What really upsets me is that while they do absolutely nothing to prevent this massive amount of spam, they're actually removing the spammer addresses mentioned in this thread "for privacy" (which is absolutely laughable, apparently they'd rather protect the privacy of the spammers than stop them from being able to spam people)
The only solution is to switch to another email service, one that actually tries to reduce spam emails and doesn't allow millions of spam emails per day with no sender address.