How Outlook’s Junk Email Filter Works

You’ve used it for years, updated it dozens of times (we hope), and have had to deal with your share of both false positives and negatives, but have you ever bothered to figure out how Outlook’s Junk Email Filter actually works? If you are like most, the answer is probably no; so in this article we are going to take a look at what, for most users, is the last technical line of defense standing between them and spam.

The Junk Email Filter is a component of Outlook that is on by default, and which processes each and every incoming email that is received, regardless of the source or type of email account. Email that is determined to be junk is delivered to the Junk E-mail folder, rather than the inbox. Periodic updates are released by Microsoft, and made available through Windows Update so that users can receive updated settings and improvements to how the filtering works.

Working with email

Any email account that Outlook is configured to use will be able to take advantage of the Junk E-mail filtering. This includes accounts using Exchange’s MAPI or OA, IMAP, and POP3 protocols, as well as Hotmail and Lotus Domino accounts when using the DAMO Connector.


The Junk E-mail filter is turned on by default in Outlook for every email account. By default, it’s set to Low, so that while it can filter out the most obvious spam, it won’t catch it all. You can adjust any of the Junk E-mail Options by clicking on the Junk button. On the toolbar Home tab, it’s in the same area as Delete. It has five tabs, including Options, Safe Senders, Safe Recipients, Blocked Senders, and International. On the Options tab, you can turn it off if you wish, or set it to High to more aggressively filter email, or even to Safe Lists Only to put all email in the Junk E-mail folder unless it comes from someone on your Safe Senders list. You can also choose to delete suspected junk rather than just filing it, or to re-enable links in suspected junk mail, if you really wish to. Don’t.

The other tabs are self-explanatory except for the International one. On that tab, you can block top-level domains for any of the country codes if you wish. You can also set blocked encodings so that if, for example, you are only conversant in English, you can block all messages that contain character sets from other languages. That won’t affect French, or German, or Australian, but it would file Cyrillic, Arabic, or Asian character sets into the Junk E-mail folder, preventing you from seeing those in your inbox.

Managing in the enterprise

If you want to push settings out to your users in a central fashion, you can use Group Policy to do so. Download the Office 2010 Administrative Template files from and then see this TechNet article on using them to configure Outlook’s Junk E-mail settings with a GPO. Just make sure you test any new GPO on a handful of users before deploying to the entire organization to make sure your settings work as you wish.

The Junk E-mail settings is another effective tool in the fight against spam. You should take advantage of any and every tool available to you, and since your users already have this in Outlook 2010, there’s no reason not to use it. Just make sure you push updates to the Junk E-mail filters as a regular part of your update process to make sure users have the latest and greatest.

Written by Casper Manes

I currently work as a Senior Messaging Consultant for one of the premier consulting firms in the world, I cut my teeth on Exchange 5.0, and have worked with every version of Microsoft’s awesome email package since then, as well as MHS, Sendmail, and MailEnable systems. I've written dozens of articles on behalf of my past employers, their partners, and others, and I finally decided to embrace blogging and social media, so please follow me on Twitter @caspermanes if you enjoy my posts.


  1. Michael · February 2, 2013

    In fact, your antispam protection can’t go without Outlook configuration. You might have deployed numerous server and cloud solutions but they can be bypassed. This is why you need to filter at the end – this is your last chance to stop spam. Of course, if the filters before Outlook don’t work as they should, you will see high levels of spam in Outlook, especially if you keep the default setting of Low.

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