Creating an anti-spoofing rule in Office365

Here's how to create a mail flow rule in Office365 to send spammers who spoof your domain to the online quarantine.  These instructions are applicable ass of 8/9/16.  Typically, these spoofed messages will go to your users' junk e-mail boxes, but this can still lead to confusion, so we don't want these messages to go to junk e-mail at all.

In the Exchange Admin Center, go to Mail Flow:

Add a new mail flow rule:

Hit More Options near the bottom of the page:

Give the rule a name of "Spoof Check."  Tell the rule to apply this rule if sender is outside of the organization and the sender's domain is [your public domain] and do the following: deliver the message to the hosted quarantine.