RentMaster has had the ability to send emails using outlook for quite a while.  From version 11, for people who dont have outlook, you can now send emails directly to your SMTP email server.

This means the email will be sent automatically without any user interface being shown.  

A default email address is required so that if the receipient does not have an email address, the email will be sent back to you instead so you are aware of the email not being sent.