1. go to space tools > permissions and remove the permission of user X to delete attachments
2. go to a page of that space which contains an attachment
3. go to attachments (no "delete" link available )
4. expand an attachment to see older versionns (including current version)
5. for each version there is the possibility to delete it
6. if you delete all versions - the attachment is gone

This completely defeats the purpose of the 'delete attachement' permission