I tried the same test and although I had the Owner and a Moderator account listening for +owner emails, I only received one email via the owner's email address. Note that both the owner and moderator accounts are both my accounts. The message was NOT sent to the group.
Although the OWNER and MOD email addresses are different, they both end up going to one GMAIL account. I think that GMAIL is intentionally only delivering one copy.
To test this, I repeated the test after adding another of my email accounts as another MOD listening to +owner messages. This account also ends up on GMAIL, but at a different GMAIL address. As expected, no message was sent to the group and I received one message in each of my gmail accounts.
So, from here it seems all is working as expected.
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Gerald
