Your whole stance looks like you have no understanding of the problems that can be faced.
Why assume the worst? More likely he wasn't inclined to go into that level of detail here.
If he's already going so far as to prevent the use of USB flash drives isn't it likely that email attachments are handled in a similarly aggressive manner (e.g. executables automatically removed, remaining attachments quarantined, etc.)? Workstation backups needn't include email; email belongs on email servers local copies are just a cache.