The default list:user:notice:welcome.txt template is confusing.
This template was based on the MM 2.1 template which mentioned unsubscribing or editing options via the web options page and "... also make such adjustments via email ...".
The web section was removed from the MM 3 template because core doesn't know the web URL or even if there is one, but it now says "You can make such adjustments via email ..." without saying what such adjustments
are.