From what I've read, a brand new member should be OK to join.? If an old member joins at Groups.io before the official transfer,? the old member settings and join date will be ignored.? These are relatively minor issues.
New posts at Groups.io before the official mirgration, from what I've seen in some groups, can cause minor issues with the message numbers.? The new posts will be numbered 1, 2, 3, 4, .., N.? The migrated posts will be numbered N+1, N+2, etc.? So if the posts are sorted by date, the numbers will be jumbled up.? So if you go to message #1 expecting the see the first Yahoo post, instead you will see the first post at Groups.io.? Also, if you scroll through the messages one by one using the < and > buttons, there will be an error message that there are no posts before the #1 message, and therefore you cannot reach the old messages from Yahoo Groups by scrolling through.? But it only affects scrolling, and you can still access the old messages in other ways (e.g. sorting by date).
You can prevent the members from posting by placing them on moderation.? There is a group setting where the first N posts from new members are moderated.
