No, email tracking status in Zoho CRM is not always fully accurate, and this isn't a Zoho-specific limitation. It's a fundamental constraint of how open tracking works across the entire email industry.
Open tracking relies on a tiny, invisible tracking pixel embedded in the email. When the recipient's email client loads external images, that pixel loads too, and this registers as an "open" back in Zoho CRM. The problem is that this depends entirely on the recipient's email client actually loading images automatically, which increasingly isn't the case.
Zoho CRM's tracking only applies to emails composed and sent from within Zoho CRM itself. Emails sent directly from Gmail or Outlook aren't tracked through this system, even if that email account is otherwise connected to Zoho CRM for activity logging.
If an email sitting in Sent status isn't opened within two days, the status automatically updates from Sent to Delivered, reflecting that it reached the recipient's server successfully even without a confirmed open. Separately, if you send an email on one day and the contact sends you an unrelated email the next day, not a reply to yours, the record's status shows as Received rather than Sent, since the system reflects whichever interaction happened most recently.
Rather than relying on the tracking pixel, Zoho CRM detects replies by monitoring the incoming email thread via your synced IMAP account and matching identifiers in the email headers back to the original message. Since this doesn't depend on image loading at all, reply detection is considerably more reliable than open tracking, and a genuine reply is a far stronger signal of real interest than a registered open ever is.