It may happen to you that Outlook blocks certain attachments, for example files with extension .exe. This is noticeable not only when you try to send mail, but also when you receive mail: you cannot open, save or even forward these attachments.

When this happens to you, don't think that you are struck by a virus. On the contrary, this is a measure which comes from Microsoft and which is meant to protect you against viruses. The reason for this behaviour is that most viruses spread by hiding in attachments to mail messages. Spreading of these viruses can therefore be stopped by blocking dangerous attachments.

This blockade is carried out most rigorously by Microsoft. A large number of files are considered dangerous and therefore will be refused. Whether a file is considered dangerous is determined exclusively by its file name extension. Examples are .exe, .bat, .vbs (Visual Basic Script) and .lnk (shortcuts). You can see the complete list at Microsoft.

 

Who is affected by this?

When you use Outlook 2000, this will affect you when you have installed Office 2000 Service Pack 2 or Service Pack 3 or just the Outlook E-Mail Security Update.
In this case undoing this behaviour is very hard; at the very least you must completely reinstall Office 2000.

When you use Outlook 2002 (Office XP) or Outlook 2003 (Office 2003), this will always affect you, since in these versions the E-mail Security is built-in and cannot be undone.

 

Can you do something about it?

Yes. There is a way to indicate that you don't want to block attachments with certain extensions. This requires editing an entry in the Windows Registry. You can do that yourself, but you can also install an addin that takes care of it for you.

If you use Outlook 2000, you should first install Service Pack 3; you can do this from the Microsoft Office Product Updates site.
In the description below we assume that you have done this.

Note. There is also a completely different way of getting around the problem. Since the only thing that counts is the file name extension, you can send forbidden attachments when you first change this extension, for example from .exe to .ex_. The recipient must save this attachment to disk and then give it back its original name.
Another method is to pack the file into a .zip-file, to be unpacked by the recipient; this works because .zip-files are not considered to be dangerous.

 

Using an add-in

A handy, and free, tool is Outlook Permissions Addin from MRH Technology Group.
This program nestles in Outlook and can be called via Tools > Options. You now have a new tab File Restrictions and there, for each extension, you can indicate by clicking whether it is Level 1 (blocked) or Level 2 (not blocked). The changes become effective once you close Outlook and start it again.

We have a local copy of the Outlook Permissions Addin which you can install directly. This way you don't have to download it; this link only works when you have logged in to the TUE-domain.

 

Editing the Registry yourself

You can also apply the changes to the Registry yourself. For each version of Outlook the procedure is slightly different. At Microsoft's web site you can find detailed descriptions for for Outlook 2000 until 2007. In short, it boils down to the following:

1. Start regedit and go to the key
   HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
   (This applies to Outlook 2003; in Outlook 2002 you use 10.0 instead of 11.0 and in Outlook 2000 you use 9.0.)
2. Choose Edit > New > String Value, type the name Level1Remove and press Enter.
3. Rightclick on this new name and choose Modify. Now enter the list of extensions that you don't want to be blocked; these extensions must be separated by semicolons, for example:
   .lnk;.url
4. Finally, click on OK and close the Registry Editor.