I own a 10 year old support yahoogroup of about 300 members and 10 moderators. We've been experiencing more and more broken functionality lately so I've been looking for alternatives and found groups.io and it looks awesome.
I've read up on the easy group membership transfer, which is nifty.
My question is : is it possible to transfer the message archive? It is pretty valuable to us. I'd be happy with just copying over all the first posts (not replies) of the 10 moderators and the owner address as a bare minimum. I have all group emails from july 2005 to april 2007 in a folder of a yahoomail account and all group emails under a label of a gmail account from april 2007 to present day. I saw tantalising mention of using hashtags to silently "load" messages into a group, but could not find further details?