Hi,
I am using Office 2010 on a Win7 system.

I've been sent 4 attachments, 3 x .XLS and 1 x .XLSX, by email, via my client Thunderbird 2.

The .XLS attachments open without issue but the .XLSX attachment, after running Excel automatically (I had to associate these files with Excel via Thunderbird), presents a warning message about possible corruption and ask if I trust the source.

What is causing this and can this message be suppressed please?

Thank you