Emails I KNOW have been opened do not show OPENED in Hubspot
I have a list pf close associates I email periodically. After emailing them I text and tell them I did so. Most say they have opened it, and Hubspot agrees with them. Some say they opened it but Hubspot shows delivered but not opened. And some cannot find the email in spam or suspect or junk folders even though Hubspot says delivered. Most of my list are on gmail, then iCloud, and then the occasion Yahoo.
Any insight into what is going on here?