I don't know why this is happening or how to stop it. Today, for the second time in about 4 months, I opened Thunderbird to find that I'd been flooded with new copies of old emails. They were all marked unread, and I did a random sampling to see that all the ones I checked I already have a copy that has been marked as read, and for some of the older ones, has been archived. Today's influx consisted of 78 messages (it was about 150 messages the first time it happened) ranging in age from last week to June of 2022. I do not believe I have changed any account settings in the last 9 months, either within Thunderbird or at Gmail, where the account is hosted. In each case all the messages were confined to one specific folder--the first time it was the Inbox folder. This time it was a sub-folder named "Receipts". If I have someohow accidentally triggered this, I'd like to know what to change in order to prevent it from happening again.