Thunderbird is deleting emails in my inbox, it only retains 14 days, this is only happening on 1 computer but not on my other one, it started randomly 6 weeks ago

Hi c.j.garaway, Since the messages are still on the server and the problem only occurs on one computer, I would first check the account settings on that computer rather than assuming Thunderbird is actually deleting the messages. Could you check Account Settings > Server Settings and tell us whether the account is using IMAP or POP? If it is POP, look at the “Leave messages on server” settings. There is an option that can remove messages from the server after a specified number of days, such as 14 days. This could explain why the other computer still has the messages locally while the server no longer does. If it is IMAP, check Account Settings > Synchronization & Storage, and also right-click the Inbox, select Properties, and check its Retention Policy. Thunderbird's IMAP retention settings can remove messages from the server, whereas simply limiting synchronization should not delete the messages from the server. Before changing anything, I would also avoid deleting or moving messages around in the affected Inbox until we know whether this is a POP, IMAP, or retention-policy issue. Could you let us know which protocol the affected computer is using and what the “Leave messages on server” or Retention Policy settings show?