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Virus scanner exclusion recommendations for Outlook

When I started Outlook this morning, it told me that it couldn’t find the pst-file that I’ve been using for years. It indeed appeared deleted and after some panicking, I found that it was luckily “only” quarantined by my virus scanner.

How do I prevent this from happening again?

Virus Scanner Exclusions buttonVirus scanners are a necessary evil. While they can protect you from malware, they sometimes can be “too smart” and can cause inconveniences or even harm your computer or data.

This is one of the reasons why it is also recommended not to let your virus scanner integrate itself with Outlook or have it act like a mail proxy. More details about that can be found in; Disable virus scanner integration?

In addition to that, you may also want to set some file and/or folder exclusions for your virus scanner as well.

Why do I need to exclude files?

Why? buttonThere are 2 main reasons to exclude certain files from being scanned by your virus scanner;

  1. Data loss or corruptions by (accidental) virus pattern recognition.
  2. Performance, stability and reliability reasons.

The first reason is the most important one but also somewhat hard to explain. Simply put, a virus scanner not only looks for actual known viruses but also at data patterns within other files which could indicate a virus. Such a pattern may for instance be found when your pst-file contains an email that contains a virus infected attachment.

While the virus is absolutely harmless within the pst-file, your virus scanner may nonetheless try to remove it from your computer and performs one of the 3 actions to do so;

  • Quarantine the entire ost- or pst-file.
  • Rip out the code-pattern and thus corrupting the file.
  • Delete the file entirely.

In some cases, such a corruption can be fixed by using the Inbox Repair Tool (scanpst.exe) but more often this leads to a total loss of the ost- or pst-file.

The second reason may be less important as computers nowadays can most certainly cope with the overhead. However, since various files are frequently being accessed or updated, there is still a performance gain that can be achieved, especially when you have a large ost- or pst-file. Additionally, a file might get locked while it is being scanned and could cause stability and reliability issues with Outlook.

Which files and folders do I need to exclude?

Which? buttonMost antivirus software allow you to set exclusions at the following levels;

  • Exclude individual files.
  • Exclude all files of a specific file type (like *.pst).
  • Exclude all files within a certain folder.
  • Exclude a process.

When it comes to Outlook, the following exclusions are recommended;

  • *.pst
    Exclude each pst-file individually or exclude the pst-file type.
    Default location: C:\Users\%username%\Documents\Outlook Files
     
  • *.ost
    Exclude each pst-file individually or exclude the ost-file type.
    Default location: C:\Users\%username%\AppData\Local\Microsoft\Outlook\
     
  • *.nst
    Exclude each pst-file individually or exclude the nst-file type.
    Default location: C:\Users\%username%\AppData\Local\Microsoft\Outlook\
     
  • *.oab
    Exclude each GUID folder or exclude the oab-file type.
    An example of a name of a GUID folder is:
    d7a2486f-c3e8-4fe3-95d8-207d213c5c92
    Default location: C:\Users\%username%\AppData\Local\Microsoft\Outlook\Offline Address Books\<guid>
     
  • *.srs
    Exclude each srs-file individually.
    Default location: C:\Users\%username%\AppData\Roaming\Microsoft\Outlook\
     
  • <profilename>.xml
    Exclude each <profilename>.xml file individually.
    Default location: C:\Users\%username%\AppData\Roaming\Microsoft\Outlook\
     
  • OutlPrnt
    Exclude the OutlPrnt file individually.
    Default location: C:\Users\%username%\AppData\Roaming\Microsoft\Outlook\

Important!
Do not exclude the outlook.exe process or the entire C:\Users\%username%\AppData\Local\Microsoft\Outlook\ folder. This will exclude too much and significantly increases the attack surface for malware on your computer.

Windows 10: How to exclude files and folders when using Windows Defender

Windows Defender - Windows 10 buttonWhen you are using Windows 10 without a 3rd party virus scanner, then you are using Windows Defender as your antivirus software. You can set the exclusions in the following location;

  1. Start-> Settings-> Update & Security-> Windows Defender
  2. Near the bottom click on: Add an exclusion
  3. Use the “Exclude a file”, “Exclude a folder” and “Exclude a file extension” buttons to set the recommended exclusions.

Virus scanner exclusions for Outlook in Windows Defender on Windows 10.
Virus scanner exclusions for Outlook in Windows Defender on Windows 10.

Note: File and Folder exclusions are mixed within the same list overview.

Windows 8: How to exclude files and folders when using Windows Defender

Windows Defender buttonWhen you are using Windows 8 without a 3rd party virus scanner, then you are using Windows Defender as your antivirus software. You can set the exclusions in the following location;

  1. Open the Start Screen.
  2. Type: Defender
  3. From the Search Results, click on: Windows Defender.
  4. Select the Settings tab in Windows Defender.
  5. Use the “Exclude files and locations” and “Exclude file type” sections in the Navigation Pane on the left to set the recommended exclusions.

Windows 7 and previous: How to exclude files and folders when using Security Essentials

Security Essentials buttonWhen you are using Windows 7 or Windows Vista, you can download and install the free Microsoft Security Essentials. You can set the exclusions in the following location;

  1. Open the Start Menu.
  2. In the Search field type: Security Essentials.
  3. From the Search Results, click on: Microsoft Security Essentials.
  4. Select the Settings tab in Microsoft Security Essentials.
  5. Use the “Exclude files and locations” and “Exclude file type” sections in the Navigation Pane on the left to set the recommended exclusions.

How to exclude files for other virus scanners

Virus Scanners buttonThere are many more 3rd party antivirus software makers like, McAfee, Norton, AVG, Avira, Avast, ESET, Kaspersky, Trend Micro, etc…

As most of them have have various editions and versions available, it is best to check the respective software maker for instructions how to set the aforementioned exclusions.


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