You have had the ability to press the Send Email button on the contact details screen for a while. This automatically opens your preferred email program with the email address filled in.
Now when you press the Send Email button, it will open a new window which will also allow you to type your email message. When you send the message, it will save this message as a note in RentHQ against the tenant or owner or contractor, and then open your email program with both the email address and the message body filled in. This enables you to keep a trail of emails send inside RentHQ itself. The email will also be in your email program under your sent items folder.
If you choose to leave the message blank, no note will be saved, and you will still be directed to your email program where you can type your message there.
Note that there are limitations with this system. Some unusual characters such as < and > and some others will be stripped out of the message before it gets to your email program, although it will be saved in the note. Also there is a limit to the maximum length of the message. This depends on your operating system and browser and email program, but generally you should be able to enter 2000 characters or more.