OutreachPlus connects to your email via API provided by Google (or Outlook). It is possible that account is not properly connected due to a network error, timeout, etc
Best way to deal with this is to simply remove the connected email and reconnect to it on Email Accounts page.
If you use a Custom option to connect your email (IMAP) please check if all details are added correctly - email, username & password, ports and if SSL is required. You can get these details from your custom email provider or your admin