To send a private email, simply compose the email as normal but include '#private' anywhere within the email subject or body. The hit ‘Send’ just like normal. The email will automatically be encrypted. Emails sent to personal email accounts (and business accounts which do not support TLS email) will be encrypted and the recipient will receive a notification email - for more information, see here. Emails sent to business accounts will be encrypted using TLS email encryption. 

Below is an example email: