When I create an email in Salesforce & add an attachment, I receive a popup warning message indicating that the attachment becomes public if I click the send button. I don't understand what this means. When I look at the attachment when it is received by the recipient, it looks like a normal attachment. When I look at the file that was uploaded to Salesforce in order to be attached, it appears to have the private sharing settings on it. Can someone explain what is meant by the warning that it becomes public? How secure is sending email attachments from Salesforce?