Sending and recieving attachments appears to be risky business these days. The recent MyDoom virus was mostly an attachment-borne virus, and it's still causing a fair amount of trouble. Unfortunately that trouble just proves the point that a lot of people still cannot be trusted to know the difference between a safe attachment, and a malicious one. To make attachment borne viruses more difficult to propagate, Outlook and Outlook Express now come configured by default to prevent access to certain...
Source: How can I send someone an attachment, if it's blocked by their copy of Outlook?
