Have you tried repairing the folder?

Thanks, will give that a try.

That is a sign of store corruption. The date is actually Zero. C++ the underlying programming language calculates all dates starting from 1 from the first of January 1969. Compacting the folder will generally fix the corruption, but mail in the folder may also be lost. SO I suggest you attempt to export any mail you want to be sure not to loose into an MBOX file using the import export tools addon before you actually compact the file. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss