Outlook Express & Blocked Attachments
Microsoft Outlook Express 6.0 SP1 introduced a new feature which blocks access to certain file types received in email messages. The main intention is to block file types which are not generally suitable for transmission by email and which are usually viruses, such as .exe, .vbs, .pif, .scr (and some others), but certain legitimate file types are also blocked, such as .pdf.
To gain access to a blocked attachment:
The list of file types is part of Internet Explorer, and the file list is sometimes updated. Therefore you may find additional file types being blocked after installing Internet Explorer updates.