So, with both options enabled (below) which one rules in case of opposite selections by Group owner and account owner?
The way I wrote it the Account setting would have precedence; the group setting would be a default applied only to accounts that had not already made a selection.
The way Pete wrote it the result would be the logical OR of the two - munge the header-from if either or both of the group and the account say to.
And, by account owner do you mean Subscription owner (for a single group) or Account owner (which is the base account of a person at groups.io?
I mean account - affecting all of the user's subscriptions. That's because the issue is a characteristic of his/her email service, affecting whether of not messages from others are delivered to him/her.