Hi,
May I know what is your CRM release and are you using IE10 or IE11?
Is it a ici Email?
Please make sure you have applied following notes.
1606884 - Attachments cannot be opened in the Draft Email
2004767 - Attachment cannot be opened due to semicolon in filename.
1591066 CRM-IC: attachments not displayable directly from IE
1514148 Attachment with EML extension not opened in outlook express
Best Regards,
Bruce