(The information in this document is specific to Outlook 2010, however the settings in Outlook 2007 and 2013 are similar. You can find information specific to other versions of Outlook with a simple Google search.)
The Junk Email Filter is designed to keep junk email messages, also known as spam, from cluttering your Inbox.
By default, the Junk Email Filter is turned on, and the protection level is set to Low, the setting designed to catch the most obvious spam. You can adjust the sensitivity of the Junk Email Filter. Messages detected by the Junk Email Filter are moved to the Junk E-mail folder.
NOTE While the Outlook Junk Email Filter protects against much of the spam sent to you, no filter can catch every junk message.
To ensure that important emails are not filtered in the future, add emails that have been put in the junk folder to the “Safe senders list”.
To add a message to the safe-send menu:
NOTE If you want to turn off the Junk Email Filter, you must also remove names from the Junk Email Filter lists.
NOTE Changing the level of protection affects only those mail accounts that deliver and save messages to your computer. This includes all email accounts that use an Outlook Data File (.pst), including POP3 and IMAP accounts. Also, protected are Microsoft Exchange Server accounts that are configured to use Cached Exchange Mode, which use an offline Outlook Data File (.ost).
NOTE When suspected junk messages are deleted, unlike other messages, they are not moved into the Deleted Items folder.