Peter,
I get the same issue with group+owner, and I use Thunderbird.
Thanks for that!
I really didn't think it was a Microsoft issue, as I think there are many group members using Outlook in one form or another, and we'd no doubt have heard of this already.
-----
With the clarity of morning comes the realization that the header To: field has the correct (+owner) address, even in the misdirected message.
So, the recommended fix to Groups.io may be, in cases where the message is delivered to Groups.io directly from btinternet.com, trust the header To field over the envelope To. Or at least compare them and make a decision.
Shal
--
Help:
/static/helpMore Help:
/g/GroupManagersForum/wikiEven More Help: Search button at the top of Messages list