Add a link to your message by Ctrl-L (Insert/Link), type "please unsubscribe" in the Link Text box, and then mailto:yourname@domain.com?subject=textstring, where textstring can be something like "Unsubscribe request", in the Link Location box. Recipients who click on the link will launch a message to you with "Unsubscribe request" as the Subject.

I don't understand what I should enter in the Link Location. I add my email address, al@pamteam.org, and then send it to another address. I click on the link Please unsubscribe, but it doesn't launch a message to al@pamteam.org

Did you enter this in the Link Location box?

mailto:al@pamteam.org?subject=unsubscribe

If the Subject contains multiple words, you may need to replace spaces with %20, e.g. unsubscribe%20request