Following Michael Hyatt‘s advice,
[...]I am now scrolling to the end of each message and clicking on the “Unsubscribe” link.
Except I used to use email addresses of the form username+tag@dom.ain where tag was different for each mailing list. This made sorting into per-mailing list folders easy, and helped track down which mailing list owner sold my address to those unsolicited commercial email senders.
Anyway, the mailing list from which I wanted to unsubscribe had a link that included the email address in the URL. I clicked the link only to discover that the mailing list site did not find my address.
Turns out the link did not change the + to %2B, which is what you need to do if you don’t want the web server to change the + to a space.
So I hand edited the URL, hit return, and bye bye mailing list subscription.
Why Pittsburgh? Well, I think the Andrew Message System was the first email system to use + in email addresses in this way. And AMS was part of the Andrew Project, at CMU.