Is there a clear rule about when the sender displays as an individual,
vs "individual via DNG<dng@???>"?

Just during this discussion I've seen it both ways. It hasn't been a
problem for me, likely because I seldom participate (that won't always
be the case), but I can see it being a hassle for a regular
contributor.

Just something I noticed, I thought I'd share in case it's helpful, I
use evolution and, every time I reply to an email from the list, it
prompts that I'm replying privately and then gives four options:
(1)reply privately, (2)cancel, (3)reply to group (goes to individual
AND mailing list), or just (4)reply to list.

Oddly it gives this option every time I reply, whether to an individual
or to individual via DNG.