Spam filtering checks for message characteristics consistent with spam.
You can change what actions to take on messages identified as spam, and choose whether to filter messages written in specific languages, or sent from specific countries or regions.
You can also turn on advanced spam filtering options if you want to pursue an aggressive approach to spam filtering.
Additionally, you can configure end-user spam notifications to inform users when messages intended for them were sent to the quarantine instead. (Sending messages to the quarantine is one of the configurable actions.) From these notifications, end users can release false positives and report them to Microsoft for analysis.
For more information, see Configure your spam filter policies. In order to help prevent spam in Office 365, use spam filtering, if you're concerned about too much spam in Office 365, use connection filtering to help prevent spam.
Checks the reputation of the sender before allowing a message to get through.
Links to Microsoft information: