The Fall '17 Sugar release featured a completely redesigned email experience. We've already posted a comparison of old-vs-new email functionality on the What to Expect page, but here's a quick overview of how you can expect emails to work going forward.
Sugar stores copies of email messages that were either sent from or archived to Sugar. You can view and work with email records much like you would work with any other type of record in Sugar.
To send mail from Sugar, users can configure one or more SMTP accounts. Any messages sent from within the application will be automatically archived in Sugar and related to the records with matching email addresses. But to view messages that aren't sent from inside Sugar, those emails must arrive in the Sugar application by one of these other methods of archiving:
For more information on all of the archiving methods and other email options, check out the recently updated Intro to Email Functionality Knowledge Base article on the Sugar Support site.