Hi,
Another way to search for your posts is to put in your last name (or maybe yahoo/groups.io user name), and search. I did this and found all my messages. If it's a common last name, you may have to pick one of yours out of the results, and then do the "All Posts by this Member" thing. If you do that, you will see that each user has an ID number and there is a search code in the box e.g. "posterid:141759" for myself.
I tried it for the OP and did a search for "Louis" and it seemed to work fine.
Searching by "poster:emailaddress" worked for me too.
It might be handy if the groups.io tech people could give as a list of codes:arguments to use in searches, e.g. "poster" and "posterid" like we have already found.
73,
Mark.
Mark - N7EKU