Why Do I Get Two Copies Of Some Messages?
TL;DR: 95033talk defaults to replying to both the group and the user, as it was setup in the original Yahoo Group. But there is a technical difference in what groups.io does that makes email programs unable to eliminate duplicate messages.
The longer version:
95033talk is setup to reply to both the group and to the sender of a post by default. For example, email@example.com sends an email to the list:
From "Bob Smith" <firstname.lastname@example.org>
Subject: Fire? Where?
Date: <<something that doesn't matter>>
Wait... there's a fire going on?
That goes out to everyone in the list. I get it in my inbox in my email program and want to reply. So I hit either the "Reply" or "Reply All" button. (This assumes I'm not using the links in the email, or replying via the groups.io user interface... those are different.) Anyway, when I hit that reply button, I create an email that says something like:
To: email@example.com, "Bob Smith" <firstname.lastname@example.org>
From "Jeff Powell" <email@example.com>
Subject: RE: Fire? Where?
Date <<something else that doesn't matter>>
> Wait... there's a fire going on?
Me too! I want to know where!
Look at the TO line in there: this email is going to both the list and directly to Bob.
That's a deliberate thing, at least for now. Imagine you only want to reply to Bob, but the list is setup to send back to only the Group by default. How would you get Bob's email address to reply to him? It may be possible - depending on your email tool and various other factors - but it's not simple. This way you have his email address right in your TO line, and only need to delete the address for the entire list.
And, of course, 95033talk is a talk group, so most replies are expected to go back to the entire list. If replies only go back to only the original sender that wouldn't be ideal either.
So it is set to send back to both the group and the original sender.
The really technical bit:
Many email programs detect when they get two copies of the exact same email and throw one of them away. In the example above, Bob will get a copy of my reply directly from me, and another copy through the group. They are the same message, so many programs will just make one disappear. And things worked like that in Yahoo Groups where this list used to be hosted.
But - for technical reasons too deep to get into here - groups.io deliberately does something to make the messages different. (For the email nerds: they change the message ID as it goes through their system.) That change means that your email software thinks the messages aren't the same, so it can't delete one, and you see both copies. The change is only in the message headers - not in the message itself - so it's invisible unless you go digging, but your email software sees it and thinks the messages aren't exactly the same.
People can avoid this when sending messages: If you want to reply to only the group - where you know the sender will see your reply as well - delete the sender out of the TO line in your email program before hitting send. And of course if you want to reply only to the sender you should delete the group email address out of the TO line.
Another wrinkle: you can reduce some of the duplicates you get by logging into groups.io, editing your profile, unchecking "My Posts - I always want copies of my own messages", and saving that change. That will avoid seeing duplicates of your own messages in some cases.