Apple Mail is hung on a message

Apple Mail is hung on a message in Snow Leopard (MacOS 10.6.8). It's not the first time.

I (rather foolishly, because it's happened before) copied-and-pasted a rather largish (15 columns and 85 rows, with lots of formatting) Excel (2008 for Mac, Version 12.3.6) spreadsheet into a new Apple Mail window. Not sending it, mind you, just composing it. The Rotating Rainbow Pizza of Death has bugged Mail ever since -- for at least three hours now. I tried Force Quitting, but Mail just started over again slowly displaying the lines of the spreadsheet -- at a rate of about 3 minutes per line. The Force Quit window shows Mail red most of the time, but black sometimes.

While it's black, the RRPoD is replaced by an arrow. I've tried to click on that message's window's red close dot, but, as soon as I do, the RRPoD reappears and nothing else happens. Once, about 45 minutes ago, after leaving the machine alone for a couple of hours, I came back to find the window's dialog pulldown asking for Save, Close or Cancel. To my regret, I clicked Cancel. The RRPoD restarted spinning. It has been spinning since.

The fact that Mail restarts whatever long, long process after a Force Quit makes this really annoying. I cannot use Mail until it finishes -- no matter how long it takes. It's been three and a half hours now.

I've looked over similar threads on these pages and I'm not hopeful to find another, faster, way out of this mess. I'll just have to wait.

But now you know -- Don't go pasting Excel spreadsheets directly into Mail. At least, not in Snow Leopard.

--Gil