I have set up a new google group, and the members mostly have non-Google email addresses. This is causing me a lot of trouble.
Two users have tried to view the group by creating a google account using their work email (by signing in and selecting "I prefer to use my current email address"). They are still unable to see the group, and the process caused their settings in the group to change to "No emails" and "Posting not allowed" - I can change the posting preference myself, but cannot change the "no emails" setting.
I tried removing one of them from the group, and adding them again. I did this once, and went back to check the list of members, and they were not there. Thinking I had missed an error message, I tried a second time, and received the message that they could not be added as they were already a member. This is a similar issue to Google Groups thinks a member I want to add is already a member but none of the proposed answers apply.
Furthermore, the person in question is receiving messages sent to the group mailing list, but they do not appear anywhere in the members list. They are effectively a ghost.
I have also seen this related issue: How do I delete a group that has hidden members? but nobody answered.
How can I get all members to be visible, and why can people not see their own account when signed into Google with their business email?