Attention: Starting December 14, 2019 Yahoo Groups will no longer host user created content on its sites. New content can no longer be uploaded after October 28, 2019. Sending/Receiving email functionality is not going away, you can continue to communicate via any email client with your group members.
Recently I downloaded the emails, pictures and files from a group. I found a Python script to do it. I couldn't get it to work with my username and password, even though I generated an application specific password for it. I did get it to work like this though:
- Log into Yahoo and join the group if you haven't already (if it's a public group you may not need to join it.
- In Chrome press F12, go to Application Tab, Cookies under Storage and click on https://groups.yahoo.com
- Find the line with T in the Name column
- Right click on the Value column and choose edit
- Copy the long string and paste it somewhere
- Repeat for the Y cookie.
- Edit the file yahoo.py and put the T and Y values into this line:
yga = YahooGroupsAPI(args.group, "T value", "Y value")
Run the script (I'm assuming you know how to do that), and you should find it downloading all emails, files and attachments.
You end up with .eml files for each email. In order to get them into something vaguely readable I used Thunderbird, imported all the eml files into a local folder, and then used the ImportExportTools addon in order to export the folder. You end up with an index.html file with a link to html emails in a subdirectory.
It would be nice if the index file had a threaded view, but that doesn't seem to be in the addon.