You should be able to join and leave a mailing list from the team page. Although the exact mechanism is undecided, one option is that the +join and +leave links would include the ability to join and leave the team's mailing list at the same time (assuming the team has a list of course, and that any beta restrictions have been determined).
There should also probably always be a big button to "Leave this mailing list" whenever you're subscribed to the team's mailing list. I don't think this should drop you on the +leave page because I think it should do the absolute minimal amount of steps necessary to unsub. Some argument can be made that it should be a one-click unsub, but I think a confirmation page is not too bad.
Additionally, this link might be more appropriate for the Unsub link in message headers and footers than the currently used https://launchpad.net/people/+me/+editemails. However if we change this, there really needs to be a generic redirect link similar to +me.
See also this thread: https://lists.ubuntu.com/mailman/private/launchpad/2008-February/024842.html
How about:
== Your involvement ==
You are a member of this team. ( Leave the team )
You are not subscribed to the team mailing list. ( Subscribe )