Safe sender and blocked sender lists in Exchange Online
As an Exchange Online or Exchange Online Protection (EOP) administrator, you can help ensure that an email message traveling through the service isn't marked as spam. One way to do this is to create safe sender and blocked sender lists for the people in your organization.
See the updated version of the tips and procedures for how to work with these lists as an admin in Prevent false positive email marked as spam with a safelist or other techniques.
If you're not an admin, and you just want to manage your own junk email in Outlook by using a safe sender list, check out the steps in this overview of the Junk Email Filter.
What is the safe and blocked sender limits in Exchange Online?
The safe and blocked sender limits in Exchange Online differ from the Active Directory and Outlook limits. They are:
Safe sender limit: 1,024
Blocked sender limit: 500
You may experience the error that is described in KB2590466. To resolve this issue, clear the "Trust emails from my contacts" check box. Alternatively, decrease the amount of email addresses that are in your default Contacts folder to bring it within the maximum allowed limit of 1024 in Exchange Online that is set for "MaxSafeSenders" attribute. For more information about this attribute and the Set-Mailbox cmdlet, seethe following topic: