SPAM Protection
Rather than try and cover this quite complex subject and redo work that has already been documented by Microsoft, here are some links to the relevant areas of the Microsoft documentation relating to this subject and it's relevance to Office365:
For end users:
- Overview of the Junk Email Filter [Outlook 2013/2016]
- Changing the level of protection in the Junk Email Folder [Outlook 2013/2016]
- Block or allow (junk email settings) [Outlook Web App]
For Admins:
- Office 365 email anti-spam protection
- Prevent false positive email marked as spam with a safelist or other techniques
- Block email spam with the Office 365 spam filter to prevent false negative issues
If you have any questions or you would like to white list a user or domain that you regularly do business with, then get in touch and as an Office 365 Administrator we can change the configuration of your organisations SPAM/Protection policy settings.