In Thunderbird the setting is in the privacy settings under Return Receipts. Other programs and webmail services have it in their settings, or ask you each time.
Tracking images work without a receipt, so they need a separate step: block remote images in your mail program. In an email tracked by HawkOpen you can also use the link “Do not track my activity” at the end of the message: opening it refuses tracking by that sender’s company at once; the company cannot switch it back.
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.