What's the difference between junk email and bulk email in EOP?

Applies to

In Microsoft 365 organizations with mailboxes in Exchange Online or standalone Exchange Online Protection (EOP) organizations without Exchange Online mailboxes, customers sometimes ask: "what's the difference between junk email and bulk email?" This topic explains the difference and describes the controls that are available in EOP.

  • Junk email is spam, which are unsolicited and universally unwanted messages (when identified correctly). By default, the EOP rejects spam based on the reputation of the source email server. If a message passes source IP inspection, it's sent to spam filtering. If the message is classified as spam by spam filtering, the message is (by default) delivered to the intended recipients and moved to their Junk Email folder.

  • Bulk email (also known as gray mail), is more difficult to classify. Whereas spam is a constant threat, bulk email is often one-time advertisements or marketing messages. Some users want bulk email messages (and in fact, they have deliberately signed up to receive them), while other users consider bulk email to be spam. For example, some users want to receive advertising messages from the Contoso Corporation or invitations to an upcoming conference on cyber security, while other users consider these same messages to be spam.

    For more information about how bulk email is identified, see Bulk complaint level (BCL) in EOP.

How to manage bulk email

Because of the mixed reaction to bulk email, there isn't universal guidance that applies to every organization.

Anti-spam polices have a default BCL threshold that's used to identify bulk email as spam. Admins can increase or decrease the threshold. For more information, see the following topics:

Another option that's easy to overlook: if a user complains about receiving bulk email, but the messages are from reputable senders that pass spam filtering in EOP, have the user check for a unsubscribe option in the bulk email message.

How to tune bulk email

In September 2022, Microsoft Defender for Office 365 Plan 2 customers can access BCL from advanced hunting. This feature allows admins to look at all bulk senders who sent mail to their organization, along with the corresponding BCL values and the email volume received. You can drill down into the bulk senders by using other columns in EmailEvents table in the Email & collaboration schema. For more information, see EmailEvents.

For example, if Contoso has set their current bulk threshold to 7 in anti-spam policies, Contoso recipients will receive email from all senders with BCL < 7 in their Inbox. Admins can run the following query to get a list of all bulk senders in the organization:

| where BulkComplaintLevel >= 1 and Timestamp > datetime(2022-09-XXT00:00:00Z)
| summarize count() by SenderMailFromAddress, BulkComplaintLevel

This query allows admins to identify wanted and unwanted senders. If a bulk sender has a BCL score that doesn't meet the bulk threshold, admins can submit the sender's messages to Microsoft for analysis, which adds the sender as an allow entry to the Tenant Allow/Block List.

Organizations without Defender for Office 365 Plan 2 can try the features in Microsoft 365 Defender for Office 365 Plan 2 for free. Use the 90-day Defender for Office 365 evaluation at https://security.microsoft.com/atpEvaluation. Learn about who can sign up and trial terms here or you can use the Threat protection status report to identify wanted and unwanted bulk senders:

  1. In the Threat protection status report, select View data by Email > Spam. To go directly to the report, open one of the following URLs:

  2. Filter for Bulk email, select an email to investigate and click on email entity to learn more about the sender. Email entity is available only for Defender for Office 365 Plan 2 customers.

  3. Once you have identified wanted and unwanted senders, adjust the bulk threshold to your desired level. If there are bulk senders with BCL score that doesn't fit within your bulk threshold, submit the messages to Microsoft for analysis, which adds the sender as an allow entry to the Tenant Allow/Block List.

Admins can follow the recommended bulk threshold values or choose a bulk threshold value that suits the needs of their organization.