Email in Zoho CRM stuck in "Sent" Status

Email in Zoho CRM stuck in "Sent" Status

We sent an email today directly from CRM (not IMAP). Usually, when we send our emails, we see a few different Statuses, such as "Delivered," "Opened," "Clicked" or "Bounced." But today we sent an email 8 hours ago and the status just keeps saying "Sent" (yes, I refreshed multiple times). Did the customer receive this email? We need to know. What does a Status of "Sent" mean in this case. Any help would be much appreciated.