Does EM Client offer a way to add an unsubscribe link into emails that I am sending out?
Sure, if the link takes the receiver to a website where they enter their email address and click an unsubscribe button. This you would do the same as inserting any link into the email body. Also possible is if the link creates a return email with unsubscribe as the subject. Again the same as inserting a link, but the link would be something like mailto:[email protected]?subject=unsubscribe rather than a url.
Both of these can be incorporated into a signature, so they could be automatically added to the email.
More usual though are links that contain the receiver’s subscription information, so that when they click on the link, it automatically unsubscribes them. This can’t be done, because it will be different for every receiver. An example is the link at the bottom of emails you receive from this forum.