Every message, inbound and outbound, is assigned a spam confidence level (SCL) based on the likelihood that the message is spam. Depending on the SCL, an inbound message may be relayed directly to the user’s Junk Email folder. All content-filtered messages are relayed to the user’s Junk Email folder by default. On outbound messages, if the SCL indicates that a message is spam, it is either routed through the high risk delivery pool, or it is bounced and not delivered. If the message isn’t delivered, the sender should receive a message, called a delivery status notification (DSN), or bounceback. telling them that the message couldn’t be delivered.
By default, the Junk E-mail Filter protection level is set to No Automatic Filtering. You can make the filter more aggressive so it catches more junk messages. The higher you set the protection level, the greater the risk of some legitimate messages being identified as junk and moved to the Junk E-mail folder.
You can tell Outlook to delete all suspected junk messages instead of moving them to the Junk E-mail folder. This takes away your ability to review messages for possible false positives, so consider the risks of using this option.
Exchange Online Protection combats malware, including viruses and spyware. Viruses infect other programs and data, and they spread throughout your computer looking for programs to infect. Spyware refers to malware that gathers your personal information, such as sign-in information and personal data, and sends it back to its author.
The EOP service offers multi-layered malware protection that’s designed to catch all known malware traveling in to and out from your organization.