With the anti-spoofing feature of Microsoft Outlook 365 for Windows or Outlook on the web, there are indicators when the sender of a message is unverified.

• There is a '?' in the sender image
   
  When Outlook can't verify the identity of the sender using email authentication techniques, it displays a '?' in the sender photo.
  
  
  If you put your mouse over the sender's name, you can see the details:
  
  Not every message that fails to authenticate is malicious. However, you should be careful about interacting with messages that don't authenticate if you don't recognize the sender. Or, if you recognize a sender that normally doesn't have a '?' in the sender image, but you suddenly start seeing it, that could be a sign the sender is being spoofed. 
   
• There is a via tab when sender's address is different than what appears in the From address
   
  Sometimes phishers try to trick you into thinking that the sender is someone other than who they really are. When Outlook detects a difference between the sender's actual address and the address on the From address, it shows the actual sender using the via tag.
   
  
  Not every message with a via tag is suspicious. However, if you recognize a message with a via tag, you should be cautious about interacting with it.