pop account? or imap? And want antivirus software are you using?

Hi Wayne, Thanks for the response. I am using pop3 with avast anti-virus

right click the folder, select properties and then repair. Lets see if it was only the index that was lost.

Many thanks Matt. All messages retrieved

I suggest you create an exception in Avast for your profile folder to prevent this occurring again.

While I can not say definitively, when you compact thunderbird completely creates a new store file for the folder and then generates an index to it. What I guess is happening is Avast is trying to scan this file as the write is occurring and the result is unsatisfactory. An exception should stop that and perhaps other random slowness you may have noticed, particularly when getting mail.

Thanks for additional advice but not sure how to create this exception. Found the location of the Profile folder with ref to Avast but I have no idea how to proceed.

I suggest you contact avast,

This might be helpful, but for instructions on actuallu using your anti virus I suggest you contact the experts in that software. The manufacturer.

Matt, Thanks for all your help. Everything seems to working ok.