J,
I think Mark has been dealing with the "multiple email address" issue
already, or has it on his Todo list.
On Trello:
Meanwhile, what can I do to help a member of both my main and my admin
group who happens to be using separate email addresses for the two
groups?
This is a tough problem for the member. It basically means that she must log out of one email address and in with the other in order to access one group or the other. Or log in using a separate browser or device for each email address -- that would be one way to avoid repeated logout / login.
Can she simply swap out her email address in one of the groups?
Not yet, pending whatever Mark does to address the problem.
She could re-join one of the groups using the other email address, so that email address ends up subscribed to both groups. But that really means re-joining it as a different person (from the group's point of view), and if the group has restricted membership she'd need to be approved under the second address.
A disadvantage to rejoining is that any content (messages, photos, etc.) she's contributed under the one email address would not be controllable by the other (different subscriber, so no delete or edit buttons). But that could be a price worth paying, depending on how annoying the current situation is for her.
Shal