[murderfs]

I have never seen anyone do that and I believe it has been literally illegal in the U.S. for the last 20 years. From https://www.ftc.gov/business-guidance/resources/can-spam-act...:

"You can’t [...] make the recipient take any step other than sending a reply email or visiting a single page on an Internet website as a condition for honoring an opt-out request."

[kragen]

this is not 'taking any step other than sending a reply email' and it's the standard way mailing lists managed with mailman or majordomo or ezmlm have worked for quite a bit longer than 20 years

also, according to that page, the can-spam act only applies to 'any electronic mail message the primary purpose of which is the commercial advertisement or promotion of a commercial product or service', not to mailing lists