Putting your queue on a ram disk would violate the rfc for an smtp server. Your smtp server is technically only allowed to say OK when the mail has been retrieved and stored on disk (not just in cache -- which is why qmail fsync's the disk before saying ok, as even if the disk crashed just after saying ok and you lost everything in the disk cache, you would still not have lost mail).

Cheers,

Alex
--
Gossamer Threads Inc.