Qmail doesn't scale well with large injection rates. Qmail scaling in that sort of manner is completely dependant upon the filesystem. Now this may have changed, but not that long back everything in submission was in one dir, processing in another dir, just like sendmail (by default) does. This caused the queue manager to stuff up something wicked at high injection rates.

Hans Reiser would argue that that reflects a limitation of the filesystem, rather than of qmail; and that apps should not have to code around such unreasonable filesystem limitations. And reiserfs goes to considerable effort to achieve good performance on directories containing thousands of small files. This would imply that if you're going to use qmail in a high-volume environment, you might consider using reiserfs, also. Jim Shankland