> maildir format scale[s] quite well; pretty much the only > limitation is storage I/O.
Depending on your FS and horsepower, anything over 1000 x (n * 10) files in a directory can start to sink you pretty quick. I've always wondered if there's a maildir split specified out there that applications could utilize... where n is your split width... tmp/n, new/n, cur/n.
