email question

Without knowing who has access to your customer's Inbox, you cannot exercise control over who reads the message. Often secretaries have full access to their manager's emails.

Apart from giving the customer a ring first and making sure he/she is sitting next to his/her workstation or laptop while you are sending the message, you can't do much.

Many companies also scan and log the contents of incoming email messages for security reasons. If the two companies exchange confidential emails, you could install security certificates in the email client application and encrypt the messages.

Even password protecting a document and attaching it to an email message gives a level of confidentiality, assuming that only the sender and the recipient know the password.