Netscape Netscape mail can't easily read a file into the message body. So you have to do it by opening data.txt in an editor, selecting the whole file, copying it, and then going to your mail message window and pasting it in. Set your mail software to use it. Receiving attachments is a different matter. Sometimes they are not using the attachment or encoding protocols your mail program expects.
Common examples are uuencoded and binhexed attachments.
Either can be decoded using Stuffit Expander on Windows or on the Mac. FTP File Transfer Protocol requires that you have access to the remote machine, either to get stuff from it or to put stuff there. Often other machines will allow anonymous access for people getting files. FTP is fast and efficient. It can be used raw , with a special program , or from within a web browser .