Guys, guys. This has NOTHING to do with replying to digests. Nothing to do with that other thread about the group member who couldn't reply to digests (which turned out to be a Thunderbird bug).
This is an iPhone bug. There are two parts to it:
1. The phone inserts the wrong email address into emails I try to send to a group, resulting in my emails bouncing from the group because that email address is not a subscriber. (In one harrowing case, it inserted my real-name email address into a message to a group that allowed posts from non-members, and in which I wanted to remain anonymous.) This is in responding to a regular, garden-variety message. Nothing to do with digests.
2. The phone leaves out the "name" part of the email address in emails it sends to me from what seem to be "noreply" email addresses. The two examples I have are (1) a groups.io email coming from [groupname]<email@example.com>. The fact that the word "digest" is in the email address has nothing to do with anything here. I was not trying to respond to it. The phone made the From address into <firstname.lastname@example.org>, leaving out the name. (2) a no-reply email from the USGS about an earthquake. I strongly suspect that the no-reply feature of the email is the criterion for when it does this.
I looked around and apparently ios14 and 14.1 (which I was updated to last night) are notoriously buggy, although I have yet to see these particular bugs reported.
Messages are the sole opinion of the author, especially the fishy ones.