What is the account type of the obsolete account - POP or IMAP?

I closed an email account which I no longer need. I knew this was going to happen so ensured the old emails were transferred to TB locally (not Local Folders).

You should have transferred your account messages to Local Folders. This is what Local Folders are for after all.

I can't see how to stop TB trying to access the server.

There is no reliable way to do that, at least not for IMAP accounts. Typically you'd delete an obsolete account in Thunderbird once all messages to be kept have been transferred to Local Folders.

Thanks for the responses. It's an IMAP Account. I'm willing to transfer the emails to local folders but at the moment it has to be one at a time and unreliable.

It may be too late for that now. IMAP works fundamentally different than POP. With IMAP all mail is managed on the server, and what you do see in Thunderbird is primarily a mirror of the messages on the server. Unless you told Thunderbird to download an offline copy of your messages from the server to your local disk, all you do have on your local disk are the message headers and eventually messages which were previously opened. Downloading an offline copy is called 'Synchronization' in Thunderbird speak. https://support.mozilla.org/kb/imap-synchronization

Since the account doesn't exist anymore on the server it is now too late to download any more message bodies.

I knew this was going to happen so ensured the old emails were transferred to TB locally

What exactly does this mean, and what did you do to 'transfer to TB locally'?

I did synchronise the account as I realised that once the account was closed I would not be able to access the emails on the server. I can see all the emails and attachments. What I hadn't counted on was the system trying to access the server every time I go to access a message or try to copy them to a structure of folders under "local folders".

I have been trying to find a way to tell the system not to try to access the server but can't see anything in Account Set-up to allow this.

Try to put Thunderbird in offline mode, and then copy over the messages to Local Folders. http://kb.mozillazine.org/Outbox#Online_and_offline_states

Christ1

Thank you very much. That works a treat. I guess I'm so used to be constantly connected that the idea of working off-line didn't occur to be.

Thank you for your help and patience.

Phil