If this is a POP account, delete the file popstate.dat.

How do I check if it is a POP account?

Tools>accountsettings>account>serversettings will probably have a line at top of server name, either IMAP Mail Server or POP Mail Server. POP accounts are those that download all mail to PC. IMAP accounts are those that keep messages online.

Thanks.

Just checked and it says IMAP Mail Server.

So does that mean there is no way for me to force download the earlier emails to thunderbirds on my laptop?

I googled download IMAP emails and I got https://www.lifewire.com/offline-imap-email-inbox-thunderbird-1173086

==

How to Access IMAP Inbox Offline in Mozilla Thunderbird

Select Tools > Account Settings > Synchronization & Storage category for the desired IMAP account. Check Keep messages for this account on this computer. Click Advanced. Check Download for the Inbox and other folders you'd like to use offline.

==

I looked at my Thunderbird settings but the Keep & Advanced > Download boxes are already ticked (checked) apart from Sent box.

Click file>offline and an option is there to force download of all folders.