Important: Please make sure that, your IMAP and/or SMTP access is enabled in your email account. And after authorization, the status is showing Authorized.
Also make sure that the Cron of RISE is activated in your server. You can setup cron from Settings > App Settings > Cron Job. Please check the official documentation of RISE of how to setup cron job.
Please remember that you'll get only unread/new emails from your main email account, but keep in mind that the process might need some moments and depending on your server's resources. It might lead to a web-server timeout.