Syncing emails to Sugar is a default feature within the CRM even if you are not using RT GSync. RT GSync automatically archives the mails you receive with corresponding contacts/leads so you can view your email history with a certain contact/lead in the emails sub-panel in the record view.
Please note email archiving comes out of the box in Sugar version 7.10 and above. For version belo 7.10 you can use RT GSync for email archiving.