The "Send Email" button will now be available from within the Sales Order. Click on this button to send emails to the contact from within the related Sales Order. More importantly, this lets you associate the sent emails to the particular Sales Order and list them as a related record under the Emails option. You now have 2 options to send emails from the sales order. While the native "Send Email" option listed under "More Options" lets you send the Sales Order as an attachment, the custom button lets you send personal emails to the contact and shows them under the related list.
This hack doesn't populate the Email address of the client automatically in the To field. You need to copy and paste it in the To field. However, this limitation can be overcome by creating an Email field in the Sales order module and adding a function (formerly custom functions) to populate contact's email id in the custom Email id field of the Sales order. This avoids the hassle of copy pasting the email id the email pop up manually every time.
Hope you found this hack useful. Check out other hacks shared in this series here.