Radiusbob has an email dropbox address for you to use to push emails from outside of Radius into your lead/client's file's Notes page. The dropbox email is found in your Account> My Information> Dropbox.
IMPORTANT:
To push a client's email response back into Radius, you'll need to reply "Thanks" or some other message and bcc the dropbox email for that reply. Unless they reply to the dropbox email address, it will not come into Radius
Email attachments will not be brought into the file's notes. The max email size to be imported into the Notes is 25 MB. If you get a bounce back from the dropbox system saying that your email was too large for import, that is why.