I would like to propose a new optional feature for Thunderbird that enhances email retention and backup for IMAP accounts. This feature would enable Thunderbird to keep a local copy of emails even if they are deleted from the IMAP server. The use case is to protect users against situations where emails might be lost due to server issues such as subscription lapses, hacking, or accidental deletion on the server side. With this option enabled, Thunderbird would maintain a local backup of all received emails independently of the server state. Additionally, it would be useful to offer an inverse synchronization option that allows Thunderbird to upload and restore emails on the server if they exist locally but are missing on the IMAP server. This two-way sync would strengthen data redundancy and improve email availability for users. This feature would provide a reliable safety net for users relying on IMAP accounts, combining local storage security with server synchronization flexibility.
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