Outlook Junk E-mail protection level changes unexpectedly to Low

Method 1: Manually set the Outlook Junk E-mail Protection option to the level that you prefer

1. On the Home tab in Outlook, click Junk, and then click Junk E-mail Options.
2. On the Options tab in the Junk E-mail Options dialog box, select the setting that you want under Choose the level of junk e-mail protection you want.
3. Click OK.

Method 2: Use Group Policy to set the Outlook Junk E-mail Protection setting to the level that you prefer

Outlook 2013 and later versions

1. Download the appropriate file for your version of Office from the Microsoft Download Center:
   
   Office 2016: http://www.microsoft.com/en-us/download/details.aspx?id=49030
   
   Office 2013: http://www.microsoft.com/download/details.aspx?id=35554
   
2. Extract the admintemplates_32bit.exe or admintemplates_64bit.exe file to a folder on your disk.
3. Copy the appropriate file to your version of Outlook to the C:\Windows\PolicyDefinitions folder:
   
   Office 2016: Outlk16.admx
   
   Office 2013: Outlk15.admx
   
4. Copy the appropriate file to your version of Outlook to the C:\Windows\PolicyDefinitions\xx-xx directory, where xx-xx is a Language Culture name. For example, for English (US), the Language Culture name is en-us. For more information about Language Culture names, see Table of Language Culture Names, Codes, and ISO Values [C++].
   
   Office 2016: Outlk16.adml
   
   Office 2013: Outlk15.adml
   
   Note The .adml file must be copied from the correct language folder.
   
5. Start the Group Policy Object Editor or the Group Policy Management Console.
   
   Note Because you may be applying the policy setting to an organizational unit and not to the whole domain, the steps may vary in this aspect of applying a policy setting. Therefore, check your Windows documentation for more information. 
   
6. In the Group Policy Object Editor or the Group Policy Management Console, under User Configuration, expand Administrative Templates, expand your version of Microsoft Outlook, expand Outlook Options, expand Preferences, and then click the Junk E-mail node.
7. Under Junk E-mail, double-click Junk E-mail protection level.
8. Click Enabled, and then select the level that you prefer under Options. Click OK.
   
   At this point, the policy setting is applied on your Outlook client computers when the Group Policy setting update is replicated. To test this change, type the following command at a command prompt, and then press Enter: 
   
   gpupdate /force

Outlook 2010

1. Download the following file from the Microsoft Download Center:
   
   https://www.microsoft.com/en-us/download/details.aspx?id=18968
   
2. Add the Outlk14.adm file to the Group Policy Object Editor or to the Group Policy Management Console.
   
   Note The steps to add the .adm file to the Group Policy Object Editor or the Group Policy Management Console vary, depending on the version of Windows that you're running. Also, because you may be applying the policy setting to an organizational unit and not to the whole domain, the steps may also vary in this aspect of applying a policy setting. Therefore, check your Windows documentation for more information. 
   
   Go to step 3 after you add the .adm template to the Group Policy Object Editor or to the Group Policy Management Console.
   
3. In the Group Policy Object Editor or the Group Policy Management Console, under User Configuration, expand Classic Administrative Templates (ADM), expand Microsoft Outlook 2010, expand Preferences, and then click the Junk E-mail node.
4. Under Junk E-mail, double-click Junk E-mail protection level.
5. Click Enabled, and then select the level that you prefer under Options. Click OK.
   
   At this point, the policy setting is applied on your Outlook 2010 client workstations when the Group Policy setting update is replicated. To test this change, at the command prompt, type the following command, and then press Enter:
   
   gpupdate /force