garbled e-mail attachments

from time to time, when sending e-mail attachments, some receipients e-mail me back to tell me that they cannot read it because everything is garbled. some of the e-mail recipients said that they don’t even get the icon that represents the attachment and it seems that the e-mail attachment somehow is received open. i have a pc running win98se and use ms outlook 2000 (ms office 2000)as the primary e-mail client. is there anything the reciepient or i need to do to fix this problem?