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My goal is to prevent our email program (Microsoft Outlook 2010) in our small office from displaying attachments in the incoming emails. I understand that some attachments may be harmless (like .jpg or .png) but due to complexity of the subject (i.e. "good" vs "bad" file extensions) for the users on that computer, and also due to multitude of ways how a program or a script can run on a Windows system, I decided to block all attachments in incoming emails.

The issue is that I can't seem to find a way to block all attachments in Outlook?

PS. OK, I can probably live with white-listing certain attachments too. Here's what I mean. Say, if I specify that Outlook can open only ".jpg;.png" attachments, it should do only that. But for ALL other attachments it should simply display a message that "attachment was blocked", and a user should not be able to override this message to open that attachment.

  • You probably can only do this from the server's end. Which email server software are you using, and do you control it? – Ƭᴇcʜιᴇ007 Feb 17 '15 at 21:43
  • @Ƭᴇcʜιᴇ007: Thanks. The mail server is Apache (not Exchange.) You see, I don't want to block the email by itself. I want it to arrive (because the attachment may be legit.) I just don't want the attachment to be openable. – MikeF Feb 17 '15 at 22:07
  • You want to allow attachments to pass through, but not be able to open the attachments? You can block from the Exchange server via Group Policy, but they can still save it to the desktop. If you want to block on the client end, there's no guarantee that they will be using Outlook. – Sun Feb 17 '15 at 22:32
  • @sunk818: As I said in a comment above yours, we're not using Exchange server. Also showing a warning but still allowing to open an attachment is not admissible (users rarely read those warnings, especially when they are shown quite regularly.) – MikeF Feb 17 '15 at 22:52
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I'm sorry to say, there is only blacklisting in Outlook. The same at Exchange server side.

Probably no one (including 3rd party Exchange server plugin providers I was able to find) found whitelisting as idea worth implementing probably because what will you do with attachment filename.qwe? There is no program in computer to open the extension so the file can be considered harmless.

So based on installed software, you have to create a blacklist. If someone finds better solution, I encourage them to post an answer here.


Outlook has capability of blacklisting of attachment types by their file extension. You can edit the blacklist to contain only attachment types you wish.. You will also need this resource.

The way of blocking fulfills your expectation I just don't want the attachment to be openable. The attachments are still in messages, but not openable.

Registry keys are:

HKEY_CURRENT_USER\Software\Microsoft\Office\XX.0\Outlook\Security\Level1Remove

file types listed in above registry key are excluded from default blacklist.

HKEY_CURRENT_USER\Software\Microsoft\Office\XX.0\Outlook\Security\Level1Add

file types listed in above registry key are included in default blacklist.

  • keys do not exist by default, you need to add them
  • key date type is String
  • list format is like this: .exe;.bat;.url

Summary: blocking and unblocking attachments can be achieved by editing lists in registry values Level1Remove and Level1Add.

  • I'm sorry, but how is it a white-listing? – MikeF Feb 17 '15 at 22:48
  • Only on Exchange server? Can you show how? – MikeF Feb 17 '15 at 22:53
  • @MikeF - You don't use exchange though. Please note this will only block the extensions you go to the effort to block. Malware can exist in ANY file extension. You might be trying to solve the wrong problem. – Ramhound Feb 17 '15 at 23:16

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