The current "rejected message" format is as below:
I see these messages because I always bcc myself on rejected messages, and every time, it strikes me as "off" that the signature on the rejection is "The Groups.io Team." I think this looks to the user as if groups.io, rather than the specific group, is responsible for rejecting the message. I think the idea was that the groups.io signature goes along with the statement at the top ("a message you sent to the group xyz") to create a frame by groups.io about the group, rather than the message coming from the specific group. However, I don't think they match, since "the moderators" refers back to the specific group, not groups.io.
I would prefer that the sig just be dropped. I don't know what a suitable replacement might be, but I don't think any sig is necessary in this notification.
Messages are the sole opinion of the author, especially the fishy ones.
I wish I could shut up, but I can't, and I won't. - Desmond Tutu