If this happened with a single email provider, it could be that they changed something without telling you, but it happening with two apparently unrelated email providers at the same time would seem to indicate the problem is on your end. I don't know what could it be if none of the things you've tried worked, though. I suggest post screenshots of your account settings, which are probably correct, but anyway just to be sure. And you may also try starting Windows (if that's the OS you're using) in <b>Safe Mode with Networking</b> mode. You may have to connect your computer to the router with an Ethernet cable, WiFi is disabled in Safe Mode: https://support.microsoft.com/help/12376/windows-10-start-your-pc-in-safe-mode <blockquote>If I delete the accounts from Thunderbird then put them in again as new accounts, will this result in loss of the all the emails from those two accounts that we have on the PC?</blockquote> When you delete a mail account in Thunderbird, you're given the option to delete only the account info (settings), or also the message data stored locally on your computer. Setting up the account again won't make Thunderbird automatically recognise the preserved message data if you didn't remove it, but you may tell Thunderbird where the account folder it didn't remove is located if you want Thunderbird to use it again. That said, this would only be a concern if you delete a POP account and you keep your mail stored in the account <i>Inbox</i>, <i>Sent</i>, etc. folders. If it's an IMAP account, everything on the server will reappear in Thunderbird when it synchronises with the server after setting up the account again. An even for a POP account, you may create folders under <b>Local Folders</b>, at the bottom of the list of accounts in the folder pane, to store and organise your mail locally on your computer there however you wish, independently of any account you may have. Mail stored there won't be affected by you deleting any account. But anyway, make a backup of your profile folder before deleting anything, just in case.