Estate Mailer Pro have the option to send this estimate to customer which is related. Also, the PDF estimate will be attached to the email. If you do not want to attach the PDF estimate, simple uncheck the checkbox Attach Estimate PDF
After sending the estimate to the customer, if you want to send the estimate again, there will be another email content. This is because the initial estimate is already sent. Now, the customer may want the estimate again and in this case, the content will be different. Go to Setup-> Email Templates -> Estimate Already Send to Client to edit the email content when sending the estimate to your customer the second time.
By default all contacts with permission estimate will be selected and you can adjust to your needs.