Custom outbound spam policies can be created and applied to specific users, groups, or domains in your organization. Custom policies always take precedence over the default policy but you can change the priority of your custom policies.
You can configure outbound spam policies in the Security & Compliance Center for organizations using Office 365 with mailboxes in Exchange Online.
How to Create Outbound Spam Policies
1. Log into O365 with an account with admin privileges.
2. Open the admin center.
3. Expand the options in the left-hand sidebar on the admin center.
4. Expand Threat Management.
5. Click on Dashboard.
6. In the Security Dashboard, click on the + New Spam Policy option in the Threat Management box.
7. On the Anti-spam settings page, click on the + Create an outbound policy button.
8. In the Outbound spam filter policy section:
-Enter a value for Name (e.g. Custom Spam Policy for Penelope).
-In the Notifications section.
--Click on the Notify specific people if a sender is blocked due to sending outbound spam.
--Click on the + Add people button and add in the email address of your O365 administrator account/s. Click the + icon to add the email to the recipient’s list.
-In the Recipient Limits section, change the value to No action, alert only for the Action when a user exceeds the specified limits field. Please note that this will ensure that the sending account will continue to send messages when it reaches the 10K daily limit instead of being blocked.
-In the Applied to section,
--Click + Add a condition.
--Change the first field to Sender is.
--For the Add a tag field, select the account used for sending an email from Penelope.
9. Click Save to save your custom Outbound spam filter policy.
10. Verify that the new policy you created is appearing on the Anti-spam Settings page and appears with On set (dark blue).