For example, Illinois State Bar Association Opinion 18-01 says that a lawyer may not use tracking software in emails to another lawyer without that lawyer’s prior informed consent. The opinion concerns specific professional situations and is not a general rule for everyone; check the rules of your own bar or chamber.
Where consent is needed, ask for it in a way that has its own basis under the rules on communications, explain what tracking records, and record the person’s active decision. In HawkOpen you can also switch tracking off for one email before sending, or exclude an address or domain from tracking.
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.