who sent mails to a much larger number of people when I was admin of a forum, I did think this had to be a top priority. And I did think it might worry new users, since I'd never seen an inbox anywhere that had just the sender's name in the sent folder, in the nearly 40 years since I first got online. There are newbies who'll be discovering the site now who don't know you're still fixing a lot of problems with the redesign. So they might think you were fine with having only the sender's name showing in the sent folder.
And DU regulars needed to know before they sent much mail to different friends here and then discovered only their own name appeared in the Sent folder. Which is why I'd posted in GD about it as soon as I spotted it - https://www.democraticunderground.com/100218385373 - to give people here a heads-up and suggest a workaround of adding the recipient's name to the mail header till the problem was fixed.
I'm not trying to be a pest. I'm trying to help, based on everything I've learned in all the time I've spent online.
When the transition to DU3 was made, were their problems similar to the ones people are having now with the new board (technical problems, not just adapting to the new design)? And if so, was there any kind of notice on every page, or at least the home page, that this is a new design and anyone encountering problems should check Community Help? Someone just discovering DU now won't have any idea that this is a new design and you're working as fast as you can to take care of any problems discovered. They might think any technical problems or serious confusion because of the design will be permanent.