Your colleague sent you a script file or HTML Help (.chm) document or even link (.lnk) to the file stored in the file server but Outlook blocks access to the file. What to do? Outlook blocks certain attachments or, rather, blocks access to certain types of received files, because of potential risks associated with these file types. The file type, indicated in the extension, a few letters following the dot at the end of filename, determines whether the file may or may not present a potential threat to the user’s security. For this, Outlook has a blacklist of potentially hazardous file types including a few dozens of items, such as .exe, .bat, and .cmd. (full list of blocked attachments can be viewed here: https://support.microsoft.com/en-us/office/blocked-attachments-in-outlook-434752e1-02d3-4e90-9124-8b81e49a8519). As you may have noticed, the key word of the paragraph is ‘potential’, and that is to say, unlike your anti-virus, Outlook can’t tell whether the file is really dangerous or not. As a result, it blocks a lot of useful files, even if they come from highly trusted senders, just to be on the safe side. The question is, why does it happen?
