I post my answer to mailing lists I ask the questions on. More than once in the last 30 years I've found my answer in the ML archive, and its sometimes still the best clue back to what to do.
ML archives last longer than specific websites, sometimes. Not always: Google is killing a lot of USENET/ML history
Mailing list archives became easier to access with services like gmane and, more recently, public inbox. I don't think they were easy to browse prior to that.
Yea. I reached a point where I decided the risk-reward was ok and deleted my local ML archives. I now check headers for the mailman/listserv link to archive and if I see it, I do make the risky decision to rely on it. Probably I'll come to regret that, in 20 years time.
ML archives last longer than specific websites, sometimes. Not always: Google is killing a lot of USENET/ML history