Blocking attachments

It may happen that Outlook blocks certain attachments, such as files with extension .exe. You will not only notice thi when sending e-mail, but also when receiving it: You cannot open these attachments, save them to disk, or even forward them to someone else.

If this happens to you, that does not mean you are the victim of a virus.
On the contrary, it is a security measure from Microsoft itself, meant to protect you from viruses. The reasoning behind it is that most viruses spread themselves by hiding in e-mail attachments. The propagation of such viruses can therefore be stopped by blocking dangerous attachments.

Microsoft applies such blockades very strictly. A large number of file types is considered dangerous, and is therefore blocked. The extension of the file name is used to determine the file type. Examples of file types that are cnsidered dangerous are .exe, .bat, .vbs (Visual Basic Script) and .lnk. The complete list can be found on the Microsoft website.

Who is affected by this?

If you use Outlook 2000, this only applies to you if you have Office 2000 Service Pack 2 or 3 or the Outlook E-Mail Security Update installed. Undoing this is difficult. It requires a complete reinstall of Office 2000, and that is not always sufficient.

If you use Outlook 2002 (Office XP) or Outlook 2003 (Office 2003), it will always apply to you, because these versions have E-Mail Security built in. It is not possible to remove it in this case.

Is there something I can do about it?

It is possible to configure your system so that files with certain extensions are not blocked. This requires editing a stting in the Windows Registry. It is possible to do this yourself, but you can also install an add-in that makes the change for you.

If you are using Outlook 2000, it is easiest by far if you make sure Service Pack 3 is installef first. If it has not been installed yet, you can install it via the Microsoft Office Product Updates site. In the instructions below, we will assume that Service Pack 3 has been installed.

Note: There is another way to work around the problem as well. Because only the file name extension is used to determine the file type, you can send 'forbidden' files if you change the extension, for example from .exe to .ex_. The recipient then needs to save the file to disk and change the name back to what it was before. Another possibility is to compress the file into a .zip file, which the recipient then needs to unpack; .zip files are not considered dangerous.

Using an add-inn

A useful, and free, tool is the Outlook Permissions Addin by MRH Technology Group. This program adds itself to Outlook, and can be configured via Tools > Options. This window will gain an extra tab, in which you can configure for every extension whether it is Level 1 (blocked) or Level 2 (not blocked). When you have changed the settings, the changes will come into effect after you close Outlook and start it again. A local copy of the Outlook Permissions Addin is available. With this copy, you can install the program directly without downloading it first. The link only works when you are logged in on the TUE domain.

Editing the Registry yourself

It is also possible to edit the Registry yourself. There are slight differences between different versions of Outlook.

1. Start regedit and find the following key:
   HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
   (This is the key for Outlook 2003; for Outlook 2002 you should replace 11.0 with 10.0, and for Outlook 2000 you should replace 11.0 with 9.0.)
2. Choose Edit > New > String Value, enter Level1Remove as the name and press Enter.
3. Right-click on the new name and choose Modify. Enter the list of extensions you don't want to block, separated by semicolons.
   For example: .lnk; .url
4. Click Ok and close the Registry Editor.