In a Workspace account where receipts are allowed, open a new message, choose More options and then Request read receipt. The recipient may be asked whether to send it and can refuse, and some mail programs never answer.
In personal Gmail, the HawkOpen extension for Chrome or Firefox adds a tracking image and tracked links to the copy of a recipient whose consent to tracking is recorded, once your company’s owner or an administrator has switched tracking on; other recipients get an ordinary email. You then see image loads and clicks with a category such as Gmail proxy or human. Every tracked email ends with a visible notice and the link “Do not track my activity”.
Where rules that require consent apply, tracking may start only after that consent has been obtained. The link in the message lets the recipient withdraw consent later.