There are several possible reasons for this, however, we would need additional information to narrow them down. What e-mail program are you using? Are you using a standard ISP, or something like AOL, Hotmail, MSN, etc.? What e-mail program is the recipient using? Is the recipient using a standard ISP, or AOL/MSN/Hotmail/etc.? If standard ISP's are used, are they blocking attachments of certain types. Some ISP's allow their users to decide whether to block certain types of attachments, others block them whether the users want them to or not. In addition, if the recipient is behind a firewall, it may be be blocking (or converting to text) the attachments.