Deploy Microsoft’s “Report Message” Add-In
Microsoft provides an add-in allowing your users to quickly report a misclassified email. We recommend deploying this for the entire tenant as described in this article:
Messages that your Office 365 email account marks as junk are automatically moved to users’ Junk Email folder. However, spammers and phishing attempts are continually evolving. If you receive a junk email in your inbox, you can use the Report Message add-in to send the message to Microsoft to help us improve our spam filters.
If you find an email in your Junk Email folder that’s not spam, you can use the Report Message add-in to mark it as a legitimate email, move the message to your Inbox, and report the false positive to help Microsoft improve our spam filters. This add-in works with Outlook 2016 and can be easily deployed for one or all users. To download the add-in, see Report Message add-in. For information about enabling the add-in, see Enable the Report Message add-in.
Enable - Report Message