Receive E-Mail digest setting pretty much sorts the problem. Generally you only get one E-Mail every day or three with all the new postings on a topic since the last digest included. So just one to skim and dump!
Far as I can see you get a new digest from Groups io
either
every time a magic number of new postings have been made
or
when a few posts have been sitting around for a few days yet the magic number hasn't been reached.
Clive