I have configured Thunderbird to download messages through pop3 and I must leave a copy of the messages on the server inbox, so I cannot delete them from the provider.
Sometimes (1 - 2 times per year) it happens that Thunderbird starts to download all the messages as if they hadn't been never downloaded.
How does Thunderbird keep track of already downloaded messages? Is there any way to avoid this messy situation?
Someone suggests to move the messages from the Inbox to an another folder but unfortunately the tools provided make this operation very time wasting.