/var/qmail

This is the qmail home directory. It must be a local directory, not

shared among machines. This is where qmail queues all mail messages. 

The queue (except for bounce message contents) is crashproof, if the

filesystem guarantees that single-byte writes are atomic and that

directory operations are synchronous. These guarantees are provided by

fixed-block filesystems such as UFS and by journaling filesystems. Under

Linux, make sure that all mail-handling filesystems are mounted with

synchronous metadata.