SMTP by itself includes no way to confirm that a recipient has opened an email message - all your server "knows" is what server it handed the email to.
Marketing software (iContact, Mailchimp) tracks email opens by embedding images, javascirpt, or fonts into the email that are downloaded from a server under their control by the recipient when they view the message. The embedded item is specific to each message and recipient, so the service knows who has accessed the embedded tracking information. Likewise, all links in the email are coded specifically for a single message & recipient so that the service "knows" if a recipient clicks on any link in a specific email.
If the recipient's email client does not download the tracking items, and the recipient doesn't click on anything, then you still don't know if they opened the email...
Another approach is to send an email that contains only a link to the actual message, which is stored on a server you control so you know when they click on the link to view the message. Or create a "secure email" account for the recipient on your server that must be used to read the email, then send only a notification to the recipient ("You have received a secure message. Please login at xxxxx to read it")
"FreeCodeCamp" released an open source email marketing delivery product a couple weeks ago:
https://github.com/freeCodeCamp/mail-for-good