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How Outlook Junk Mail filter works

You should know about some basic points of how filtering works before you start setting up the Outlook Junk Mail filter. In this post, we are going to tell you just a few facts that you should check before you start configuring the filter settings or you should remember.

How Outlook Junk Mail filter works-step-1


E-mail account types supported by the Junk E-mail Filter are-

  • Exchange accounts in Cached Exchange Mode
  • Exchange account that delivers to a Personal Folders file (.pst)
  • HTTP (Windows Live Mail) account
  • POP3 account
  • IMAP account
  • Microsoft Office Outlook Connector for IBM Lotus Domino
  • Outlook Connector for MSN

How the Junk E-mail Filter works

The Junk E-mail Filter evaluates each incoming message to assess whether it may be spam, based on several factors. These can include the time when the message was sent and the content of the message. By default, the Junk E-mail Filter is turned on and the protection level is set to Low. This level catches only the most obvious spam. You can make the filter more aggressive by changing the level of protection. Also, the Junk E-mail Filter can be updated periodically to protect against the latest techniques that spammers use to spam your Inbox.

NOTE: The Outlook Junk E-mail Filter does not stop junk e-mail from being delivered, but rather diverts suspected spam to your Junk E-mail folder instead of your inbox. Some third-party solutions are available which can be more aggressive on this front.

TIP: You can control many of your Junk E-mail Filter settings in the Junk E-mail Options dialog box. From your Inbox, in the Actions menu, point to Junk E-mail and then click Junk E-mail Options.


There are five different user-controlled lists that can determine whether your email will hit the junk folder or not:

  • Safe Senders List – Email addresses and domain names in this list are never treated as junk. All names and addresses in the global address list (GAL) in a Microsoft Exchange Server account are automatically considered safe.
  • Safe Recipients List – Users can add the mailing lists and distribution lists that they are part of to this list so that they will never be marked as spam.
  • Blocked Senders List – Once users add an email address or domain to this list, messages from that source are automatically sent to the Junk Email folder.
  • Blocked Top-Level Domains List – To block messages from another country or region, users can add country/region codes to this list.
  • Blocked Encodings List – To block messages that contain another character set or alphabet, users can add encodings to this list.

By default, the Junk Email Filter is turned on the “No Automatic Filtering” level. However, users have the ability to easily change the level of protection and make it more or less aggressive. Here are the options were given:

  • No Automatic Filtering – Turns off the automatic Junk Email Filter, but messages are evaluated using the domain names and email addresses in users’ Blocked Senders Lists.
  • Low – Filters only messages that are most obviously junk.
  • High – Filters all messages suspected as junk.
  • Safe Lists Only – Any message that is sent from someone not on your Safe Senders List or to a mailing list on your Safe Recipients List is automatically classified as junk.
  • Delete All – Users also have the option to delete all suspected junk messages instead of having them moved to the Junk Email folder.

In addition, if users have an Exchange account, they have two other junk-fighting tools-

  • Cached Exchange Mode or download to an Outlook Data File (.pst) – If you use either of these, your Junk Email Filters Lists are available from any computer and used by the server to evaluate messages.
  • Working Offline – If you work offline, your Junk Email Filters Lists will still be saved on your server and are available from any computer if you have the Junk Email feature enabled in Outlook Web Access or Outlook Web App.

Video Demonstrating How Junk Email Filter Works in Outlook

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  • ravi lodhi

    It;s a great analysis for this topic

  • Gaurav Singh

    Is it 100% efficient to block all suspicious mail or it have some loopholes ?

  • rahul singh

    all of my junk email has suddenly started coming into my inbox. I have checked my filters and they are set to exclusive. I even tried setting them to normal and then re-setting them to exclusive, but it hasn’t worked.

  • John Abram

    What is POP3 Account and what is a work of POP3 account.please explain

  • William Brown

    how do i avoid junk filters ?

  • Roman Miller

    any email account type which is not supported by filter?

  • Phillips

    sometimes spam mails are delivered to inbox why ?