In fact Outlook Express does not delete any attachments, not before SP2 and not afterwards either. What it does do is block access to attachments that might potentially contain a virus. The warning that appears in the InfoBar when you open a message states this quite clearly. But surprise and frustration often cause people to miss the part about "access" and so jump to a faulty conclusion. Furthermore, if you normally read messages only in the Preview pane, you will see only a grayed-out icon as your only clue that access has been blocked.
 
The InfoBar tells you access to an attachment has been blocked.

The InfoBar tells you access to an attachment has been blocked.

The Preview pane gives only a visual clue that blocking has occurred.

The Preview pane gives only a visual clue that blocking has occurred.

This feature is not really new in SP2. It has always been present in Outlook Express 6, but it was disabled by default until Windows XP Service Pack 1. Since then all subsequent updates, including SP2, have turned on the block automatically. E-mail attachments remain the most common route for computer infections, and that is likely to remain true for the foreseeable future. But contrary to urban legend, it has been years since a virus could run automatically simply by a message being viewed. Today the only way a virus in e-mail can infect your computer is if you actually open the infected attachment. And once that infection occurs, the virus, worm or Trojan Horse will begin sending more copies of itself to people in your address book, thus appearing to come from you or from one of your contacts. This bit of social engineering is designed to trick the recipient into thinking the attachment is safe, and so makes it more likely he will open the attachment, thus exposing all his contacts to the same shenanigans. This exponential spread of malware means that protecting your computer is not just a personal issue anymore. It affects all of us who enjoy the Internet. It may take an entire village to raise a child, but it takes only one person opening the wrong attachment to launch a world-wide onslaught of the latest malware. Outlook Express in SP2 makes it far less likely that that one person is you.
 
TipTip: Some attachments are always dangerous!

Microsoft never sends updates to customers in e-mail. Anti-virus vendors never send updates in e-mail. In fact no reputable Internet company should send files in e-mail unless you have requested them to do so. But many viruses arrive in e-mail that looks like it came from Microsoft, or Norton, or McAfee, or eBay. If you receive an e-mail attachment you didn't request that seems to come from a known and reputable company, don't even bother to scan it for viruses. It is probably a virus, or a worm, or a Trojan Horse, or a scam to get your credit card number, or some other form of malware. My advice is just delete it, right now.
 
Risk Level and File Types
Outlook Express does not block all attachments indiscriminately. After all, some file types simply cannot contain a virus, such as a plain text or image file. To determine if an attachment might potentially contain a virus, Outlook Express checks the attachment's extension (the 3 letters after the filename) and sees if it is on the list of high-risk file types. These are the executable files such as *.exe (executable), *.pif (program information file), *.scr (screen saver), *.vbs (Visual Basic script), and 67 others. If the extension is high-risk, Outlook Express blocks all access to the attachment. If the extension is one of the 16 or so low-risk types, such as *.txt, *.bmp, *.jpg and *.gif, the attachment is not blocked. If the extension is neither high- nor low-risk, it is considered, not surprisingly, medium-risk. Outlook Express will then give you a warning if you try to open the attachment, but will not block it completely. While some of us might find it fun to try guessing all 71 high-risk file extensions, Microsoft has already given us the cheat sheet, along with more technical detail.
 

Unblocking an Attachment

E-mail attachments might be dangerous, but they can also be useful, fun, and sometimes even necessary. How do you turn off the block? The answer is just a few mouse clicks away: not so many as to be a burden, but not so few that you can open an attachment without a few seconds to consider if you really should.
To turn off the attachment block long enough to access an attachment:
 
Click Tools.
Click Options.
Click the Security tab.
Clear the check box next to "Do not allow attachments to be saved or opened that could potentially be a virus."
Click OK.
 

The Security Options panel allows you to turn off  blocking of attachments, as well as blocking of automatic downloads.

The Security Options panel allows you to turn off blocking of attachments, as well as blocking of automatic downloads.

Note that any change you make here will not affect a message that is already being displayed, either in the Preview pane or a message window. In that case simply select another message and then click again on the one with the attachment, or close and re-open the message window.
 
So far, so good. You now have access to the attachment and can save it to your hard disk and scan it with your anti-virus program (with the latest signature files of course.) But before you go any further, be sure to return to the Security Options panel and turn the block on again so you will be protected in the future.
 
Opening a File Saved from an Attachment
Now that you have the attachment saved and scanned, you probably want to open the saved file. At this point SP2 behaves quite differently than before. Previously you could simply open the saved file and it would run like any other file. SP2 adds a new layer of protection in that it remembers the file you are trying to open was downloaded from the Restricted Zone (the default setting for Outlook Express) and so you are given one more warning.
 
Trying to open a file that was saved from an attachment results in a firm warning for SP2 users.

Trying to open a file that was saved from an attachment results in a firm warning for SP2 users.

If you are sure the file is legitimate and that it is not a virus, you can clear the check box for "Always ask before opening this file" and Windows will treat the file normally.
 
TipTip: An easy way to unblock multiple saved files

If you receive an e-mail message with several attachments that have been blocked, there is an easy way to unblock them all at once after you save them to your hard disk. Hold the CTRL key while you click once on each saved file until all are selected. Then right-click on any one of them and click Properties. You will see a new option at the bottom of the General tab.
 
Unblock one or several files at once using the Properties dialogue.
Unblock one or several files at once using the Properties dialogue.

Click the Unblock button and all the files will be available to run as normal files.
Sometimes you might receive an attachment that you are sure is safe because it passes the safe-computing basics:
the attachment came from a known source and
you were expecting it and
you know what the file will do and
your anti-virus program is up to date and it is configured to scan executable files when they are opened.
 
In that case you can open an unblocked attachment directly in Outlook Express. You will receive a warning similar to that when you open a saved file, but without the option to unblock the file permanently. You will continue to receive the same warning each time you try to open the attachment in Outlook Express.

"Outlook Express Won't Let Me View Pictures"

The second feature in SP2, this one brand new, that has also caused some misunderstanding is the block on automatic downloads of images and other external content in HTML e-mail. As the use of e-mail has grown, so too has the amount of spam, including pornographic images, money-making scams, and other assorted junk. Much of the spam includes Web beacons (also known as Web bugs), used on some Web sites to track visitors, but used by spammers to verify e-mail addresses. By blocking automatic downloads of such external content, Outlook Express now protects you from viewing offensive and possibly illegal images while simultaneously preventing spammers from verifying your e-mail address. The block is also an advantage for those who use dial-up connections and might be viewing messages while offline. Prior to SP2, Outlook Express would launch a dial-up connection in order to download the external content. By blocking automatic downloads the user has more control over dial-up connections, and hence more control over phone costs.
After installing SP2 you can see immediately if Outlook Express has blocked any external content in a message because the InfoBar will appear above the message body telling you so. To download the blocked content, all you have to do is click on the InfoBar. Should you wish to turn this feature off, you can do so easily in the Security Options (the second item in the Security Options panel shown earlier.)
 
To download blocked images and other external content just click the InfoBar.

To download blocked images and other external content just click the InfoBar.
 
Note: Extracted from Microsoft Internet Explorer Community Column

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