Maria,
I wrote:
If you customize the group's Welcome message before the transfer then
it will be sent to each member as they are added to the Groups.io
group.
And, of course, I do plan to send a Special Notice to the Yahoo Group before starting the transfer - perhaps a day or so before, to give the Yahoo Group members a heads-up on what's happening.
I'll probably say much the same things as mentioned in the customized Welcome text, but written from the pre-transfer point of view.
Note to self: don't forget that Special Notice.
Shal
Shal Farley