When a CCtoMany discussion list distributes a message, the From: header identifies the author of that message. Unfortunately, because of modern email DMARC policies, many larger ISPs now prohibit the use of their domain in the From: address unless THEY have sent the message.
So before distributing a message to your discussion list, the CCtoMany list manager will rewrite the From: header to include a readable version of the author's address but using the email address of your list. Where your members previously saw something like this on received messages:
From: Byron Lunz <email@example.com>
... they will now see this:
From: Byron Lunz (byronl at gmail.com) via listid <firstname.lastname@example.org>
The author's email is shown as part of the From header's "real name" portion, and the list address appears in the email address field. Recipients will still see the author's name and they can deduce the email address if needed. Depending on the policy of your list, replies will then go to either the original author only, or back to the entire list, just as before.