Some time in the early 60s, my dad took me to see a movie that I think may well have been filmed in these tunnels. Some digging on IMDB reveals it was a National Film Board of Canada movie made in 1947 and directed by Leslie McFarlane, called "The Boy Who Stopped Niagara." Anyone else seen it?

Discovered exactly the same thing this week after reinstalling my OS and copying over my old mail folders. It seems odd to me that Thunderbird would retain messages that are explicitly deleted, but I was finding stuff that was more than three years old in there.

On the other hand, I only reclaimed 40Mb so I obviously get nowhere near the amount of mail you do!

Thanks to Frumious for the tip, settings duly changed.