[wakeupcall]

Open mailing lists often have public archives, for example https://www.mail-archive.com/. Many lists are subscribed to multiple public archives.

Those archives are often searchable on their own platforms, and are indexed by regular search engines too.

Now about mailing lists created using the google "groups" platform itself, is a different story. Does google index it's own group archives? No idea. Those were _already_ horrible to look at before and I've subscribed most of the ones I follow to other public archives to get something usable.