What's the difference between junk email and bulk email?
Customers sometimes ask "what's the difference between junk email and bulk email messages?" The purpose of this topic is to explain the difference and to provide information about the different options that are available for both in Exchange Online and Exchange Online Protection (EOP).
What's junk email?
Junk email messages are "spam" messages, which are unsolicited (and typically unwanted) email messages that are filtered by the service. By default, the service rejects the spam message based on the reputation of the sending IP address. However, if it passes IP inspection but is classified as spam by the content filters, the message is sent to the Junk Email folder of the intended recipients.
The action performed on content-filtered messages is configurable via content filter policies in the Exchange admin center (EAC), as described in Configure your spam filter policies. Also, if you disagree with the spam classification, you can report messages that you consider to be spam or non-spam to Microsoft in several ways, as described in Submit spam, non-spam, and phishing scam messages to Microsoft for analysis.
What's bulk email?
Bulk email, also referred to as gray mail, is a type of email message that's more difficult to classify. Whereas junk email is a constant threat, bulk email is typically comprised of an advertisement or marketing message that's not likely to get sent repeatedly. Bulk email is wanted by some users, and in fact they may have deliberately signed up to receive these messages, while other users may consider these types of messages to be spam. For example, some users want to receive advertising emails from the Contoso Corporation or invitations to an upcoming conference on cyber security, while other users consider such emails to be spam.
How to manage bulk email
How to manage bulk email isn't a clear cut decision, because if all bulk email is classified as spam, the users that want it may complain and submit it as a false positive (non-spam) message that was wrongly marked as spam. On the other hand, if all bulk email is let through, the users that don't want it may complain and submit it as a missed spam message (false negative) that wrongly arrived in their inbox.
Enable bulk mail sensitivity control in the content filter policy
Depending on your company's policy on bulk email messages, admins can select a threshold to assign the bulk email. The setting is configurable via content filter policies in the EAC. Check out Configure your spam filter policies for the steps. You can choose a threshold setting from 1-9, where 1 marks most bulk email as spam, and 9 allows most bulk email to be delivered. The service then performs the configured action, such as sending the message to the recipient's Junk Email folder.