first of all, people who were never part of a group members cannot see or write to that group. i changed the title accordingly to not be misleading for new users that may not have full context.
to the question: groups in delta chat are meant for friends, family, trusted people. people becoming toxic afterwards, is tempting to discuss, however, this is not only a technical problem.
but still, on the technical side things improved a lot: yes, it was hard to leave a group in the past (“group californication”, we had call it). as we do not use a central server to manage groups, different members easily saw different “truths” of the memberlist. in turn, resulting in removed members being re-added.
recent versions got a new, improved group membership model, meaning all members now see the same memberslist, making re-adding more unlikely - it still can happen, though, as the consistent memberlist rules removals afaik - but then another removal should do.
note, the new model may not be rolled out fully yet, so some members may have the old model still. surely, there may be bugs, we are happy to get reproducible, actionable reports.
EDIT: i just tested, non-group members are not re-added when they post again, but marked by ~ before the name (similar to whatsapp & co). on non-toxic situations, this is on purpose, eg. when messages are forwarded in support channels - still these answers need to know the original group
finally, there are lots of ongoing discussions to extend the groups to moderation, that makes toxic members in a group then more managable, we’ll see what comes here. as usual, as we have very few resources, we try to be driven by real-world needs.
