Spam filter settings include selecting the action to take on messages that are identified as spam. Spam filter policy settings are applied to inbound messages only and there are two types:
Default: The default spam filter policy is used to configure company-wide spam filter settings. This policy be renamed and is always on.
Custom: Custom spam filter policies can be granular and applied to specific users, groups, or domains in your organization. Custom policies always take precedence over the default policy. You can change the order in which your custom policies run by changing the priority of each custom policy; however, only the highest priority (i.e. number closest to 0) policy will apply if multiple policies meet the criteria set.
How To Create A New Spam Filter
Go to your Admin Centre. Click on Exchange.
Click on Protection, then Spam filter option, and then finally click on ‘+’ sign.
Under the Spam option, you can see there are two options:
Spam: it says that it is very likely that the message you received is spam.
Highly Confidential Spam: Means that Microsoft is sure it is a spam.
In both of these options, there is a dropdown from which you can choose. Choose one of the options. The options are summarised below:
Configure Select the threshold to determine how you want to treat bulk email as spam, based on the Bulk Complaint Level (BCL) of the message. You can choose a threshold setting from 1 to 9, where 1 indicates most bulk email as spam, and 9 allows the most bulk email to be delivered.
For custom policies only, click the Apply to menu item, and then create a condition-based rule to specify the users, groups, and domains to which to apply this policy. You can create multiple conditions, if they are unique.