Thunderbird occasionally “Automatically downloads all (not just new) messages from the POP server. The number of download messages are based on the client server settings “leave messages on server” and “for at most <number> days”. This has happened several times (maybe eight, with four different accounts and two different POP servers) within about a month. Nothing “I have” changed around that time; maybe some automatic updates or server-side changes I haven’t kept track of. To clean up the Inbox To remove the hundreds of re-downloaded old messages as new: 1. Upon discovery “sort by read” and select and move to new folder. 2. Then “sort by date” looking for matching date & times and then matching subject. 3. When found identify by comparing that time with the time found by selecting View > Message Source (or Ctrl+U), the first line contains either the original same date or a different recent redownload date. 4. Move original message back to Inbox. Once complete delete all remaining redownload messages which all should have the same first line date & time when viewing Message Source info. Doing this every few weeks is becoming a pain this last month or so. Leaving messages on the server for a few months is required for recovery if required. Have been operating this way with TB since 1999; excite@home days.