Dean,
On my group some see that post have via Groups.io attached to their
emails. Why is this only on some emails and not all.
It's the DMARC thing. Some email services attempt to prevent delivery of messages from their users if the message did not come directly from one of their servers.[1] It is supposed to prevent spoofing (and phishing and other forms of fraud).
So for users of those services you will see
From: user via Groups.io <user=yahoo.com @ groups.io>
instead of the usual
From: Display Name <user @ example.com>
Modifying the email From address in this way side-steps the email service's instructions to reject messages that claim to have come from their service but didn't arrive directly (e.g. came via a list).
I know one member post twice, once post from with in the group
itself, and one wasa reply sent through her email account she where
she replied. Yet both has the via Groups.io
Hmm... That modification might not have been needed when posting using the group's pages. Not sure about that.
Another member who post should show
hername@... are coming as
hername-aol.com@...
Then it looks like AOL is a service that has set a "reject" policy for messages that pass through email lists. Yahoo Mail is also such a service, there may be others.
You may have noticed that Yahoo Groups does a similar modification, but they do it to all members' addresses, not just the ones that need it.
-- Shal
1: It is more complicated than that, but that's close enough for our purposes.
Shal Farley