Fighting Junk Email

Microsoft's email safety roadmap involves an unmatched cross-product approach. SmartScreen® anti-spam and anti-phishing filtering technology is being applied across Microsoft's email platforms to provide customers with the latest anti-spam and anti-phishing tools and innovations throughout the network. These products include, Exchange, Office 365, and more.
The goal for is to offer a comprehensive and usable email service that helps detect and protect users from junk email, fraudulent email threats (phishing) and viruses.

The Challenge

Email has become an important communication tool not only for consumers but also for marketers, support staff, sales organizations, and businesses of all sizes. As email use has grown, so has email abuse. Unmonitored junk email can clog inboxes and networks, impact consumer satisfaction, and hamper the effectiveness of legitimate email communications. While technology alone cannot solve the problem, it is a critical component in our comprehensive anti-spam approach. That's why Microsoft continues to invest in research and development to advance anti-spam technologies. Simply put, it starts by containing and filtering junk email.

Our Efforts

We offer a number of steps to minimize the negative impact junk email has on our users' email experience. For example, we've implemented a number of mechanisms to reduce the burden of junk email which currently prevents nearly 4.5 billion email messages from reaching users every day!

Junk Email Filters

Microsoft SmartScreen®

To help reduce the consequences of junk email, includes junk email protection using patented SmartScreen® technology which screens email to identify and separate junk email from legitimate email. Based on Microsoft Research's patented machine-learning technology, the SmartScreen® content filter learns from known spam and phishing threats, user feedback, as well as from users who have opted to be part of our junk email classification program. These types of data help train SmartScreen® how to recognize legitimate email and junk email and are key inputs into sender reputation. Machine learning refers to the probability-based algorithms that are used to distinguish between the different characteristics of legitimate and junk email. Ongoing feedback from customers in the junk email classification program helps ensure that the SmartScreen® technology is continually trained and improved.

How does it work?

When an external user sends email messages to an account, SmartScreen® filter technology evaluates the content of the messages and assigns the message a rating based on the probability that the message is junk email. This rating is stored as a message property called a spam confidence level (SCL) within the message itself. The SCL rating stays with the message as it is sent to other anti-spam protection layers within
Rules inside are set to handle email messages with various SCL ratings. If a message has an SCL rating lower than a certain threshold, it is considered spam and a rule then deletes the message rather than send the message to the users' junk email folders. If the message has a higher SCL rating than the threshold, the email is delivered to the user's junk email folder rather than to the inbox. Filters

In addition to the anti-spam filtering technologies, also gives each user the ability to set filter levels to further improve the delivery of email to their account. Users can easily add a sender or domain name to the Safe Senders and Domains List so that the email from that sender or domain is never treated as junk regardless of the content of the message. Conversely, users can enable "exclusive" mode to accept only messages from the Contacts and Safe Senders List.
Email messages from a certain email address or domain name can also be blocked by adding the sender to your Blocked Senders List, or by clicking "Mark as junk" in the client. In addition, when a message is reported as junk email using the "Junk" reporting button in, we use this feedback from our users to help determine if future messages from that sender should be blocked or filtered automatically.

Phishing Protection

Phishing (pronounced "fishing") is a form of identity theft and one of the fastest growing threats on the Internet. You can often identify a phishing message by the fact that it requests personal or financial information or includes a link to a website that requests such information. offer phishing protection as part of the patented SmartScreen® filter technology. SmartScreen® analyzes emails to help detect fraudulent links or spoofed domains to help protect users from these types of online scams.

How does it work?

Often a phishing email will be sent containing a link, once clicked it will redirect users to a fraudulent web site appearing to be valid (like your financial institution or online service).  This phishing site usually prompts users to enter personal information like user names, passwords and/or social security numbers. Any information entered on the phishing site helps the phisher steal your identity. By using well-known trusted brand names and logos, phishers are able to appear legitimate. Microsoft's SmartScreen® phishing filter technology offered in checks for potential phishing characteristics in email.  If found, the email is either deleted or a warning is given via the Safety Information Bar.
Microsoft is focusing its anti-phishing technology efforts on two fronts: first by helping to prevent phishing email messages from reaching our customers and secondly helping to eliminate the possibility of customers being deceived by spoofed emails and web sites. Internet Explorer version 7 and above will block or warn users when they visit known or potential phishing sites so that they aren't tricked into providing personal information.


Domain spoofing is a way of imitating a legitimate email address to make fraudulent email look legitimate. Spoofing is used by malicious individuals and organizations in phishing scams to lure people into divulging sensitive personal information. Disclosure of such information can lead to identify theft and other types of fraud. uses the Sender Protection Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC) to verify that messages came from the domain they claim to come from. We recommend that all senders use SPF and DKIM to protect their recipients from junk email and phishing scams. Beyond that we recommend senders consider publishing a DMARC to reject or quarantine mail sent from unauthorized senders.
To learn more about SPF, please read RFC 4408
To learn more about DKIM, please read RFC 4871
To learn more about DMARC, please visit

How does it work? uses domain, IP, and authentication results as part of our SmartScreen® junk email filters. Once the sender has been authenticated, the results may then be cross-referenced to past traffic patterns and sender reputation. This makes it possible to block not only junk but phishing scams as well.

Trusted Sender

In order to further protect users from phishing attacks, marks messages from some authenticated senders as "trusted" in the interface. This is neither an endorsement of any particular sender, nor is it guarantee of delivery. Rather, it simply tells our users that the message in question actually came from the purported sender. The list of domains in this program is determined solely by the team. We will continue to expand the list as appropriate to protect our users, but we are not accepting applications from individual senders to join. We use the following criteria when considering which domains to add:
  • The domain must already be spoofed in phishing attacks against users
  • The domain must send messages with sensitive transactional contents
  • The domain must send large volumes of mail to
  • The domain must use SPF or DKIM to authenticate messages

Unsubscribe provides an "unsubscribe" option in our interface, which allows users to stop getting mail from a particular sender. Clicking unsubscribe adds the sender to the user's block list, to ensure no more email will be received. If we recognize the sender, and know they have a history of good sending practices, we'll also ask them to remove the user from their mailing list, so the senders know not to keep trying to send to that user.
In order to receive unsubscribe feedback, senders must include an RFC2369-compliant List-Unsubscribe header containing a mailto: address. Please note that we only enable this feedback via email, so URIs for other protocols such as http will be ignored. The sender must also have a good reputation, and must act promptly in removing users from their lists. We do not provide unsubscribe feedback to senders when a user unsubscribes from an untrusted message.
To learn more about List-Unsubscribe please read RFC2369


At Microsoft, we believe that the development of new technologies and self-regulation requires the support of effective government policy and legal frameworks. The worldwide spam proliferation has spurred numerous legislative bodies to regulate commercial email. Many countries/regions now have spam-fighting laws in place. The United States has both federal and state laws governing spam, and this complementary approach is helping to curtail spam while enabling legitimate e-commerce to prosper. The CAN-SPAM Act expands the tools available for curbing fraudulent and deceptive email messages.
While legislation is important, it is only one part of a strategy to fight spam. Other means to fight spam include developing improved spam-fighting technology, implementing industry best practices and junk email reporting methods, educating email users, and prosecuting spammers.