This just means that opening these with require going back to the server to pick up the rest of the message. Outlook does that for you. Select a message. The beginning of the message appears in the Preview Pane below the list of messages. Notice the large paperclip to the right.
Attachments are items , such as computer files or imbedded objects .
Computer files can be as benign as a text-only copy of a word processing document or a photo of your grandchild or as potentially dangerous as the executable code for a program. At one time, actually downloading an infected file from a network distributor was the most common method of acquiring a virus. The virus waited for you to come for it. Today, the preferred method of distribution is to send it out to you either as an attachment, or as an integral part of an e-mail document, formatted as a Word document. That's one reason we ask you to set your Mail Format to Plain Text .