I manage this in the listserv groups I admininster by not automatically
removing a first poster from moderation. I wait until they have made
additional posts, each of which is reviewed and approved if it is real. If
they they truly belong they are removed from moderation. I used to manage
my Yahoo groups the same way. Is there an easy way to do that with gio?

Select this checkbox if you want to approve the first message or first few
messages sent to the group by new members. This setting allows you to
check that new members follow your group’s requirements for posting
messages.

An option from the list to specify whether new members automatically are
no longer moderated after they send one approved message or after they
send two, three, or four consecutive approved messages. Or you can select
Not enabled (which is at the top of the list) to keep new members
moderated until you decide to unmoderate them manually