well this server should be able to cope with quite a high volume of email, only problem I'm seeing at the moment is broken image thumbnails for new image uploads.
I'm currently rebuilding all the thumbnails on the server to see if that fixes it! this may take a few hours!
Update
62,355 image thumbnails rebuilt, 30k or so still to go
and yes this will be effecting the speed but I bet it still seems faster
Update
The rebuilt thumbs all have the same problem now so I'm working on a fix