I experimented using the folder retention policy for emails. I left 'Always keep starred messages' checked so that I could set either 'Delete all but the most recent N messages' or 'Delete messages more than N days old', but I discover that when a folder fills up with starred messages, new messages get immediately deleted. I need the retention policy to keep starred messages but ignore starred messages when applying the either the 'Delete all but the most recent N' or 'Delete message more than N days old'. I use starred messages sot that I can keep them long-term / indefinitely. I need the retention policy - for unstarred messages - that I need. So that if I select 'Delete all but the most recent 30 messages' and the folder has 100 starred messages, it will keep the 100 starred messages but only keep the most recent 30 unstarred messages. In addition to the 100 starred messages. Likewise if I select 'Delete messages more than 100 days old' and the folder has 200 starred messages, then the starred messages will be kept no matter how old they are (i.e. indefinitely) but the oldest un-starred message in the folder will be at most 100 days old, and the older starred messages will be kept.